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Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by T.J. Mercier

On Tue, Jul 30, 2024 at 1:14 AM Huan Yang <link(a)vivo.com> wrote: > > > 在 2024/7/30 16:03, Christian König 写道: > > Am 30.07.24 um 09:57 schrieb Huan Yang: > >> Background > >> ==== > >> Some user may need load file into dma-buf, current way is: > >> 1. allocate a dma-buf, get dma-buf fd > >> 2. mmap dma-buf fd into user vaddr > >> 3. read(file_fd, vaddr, fsz) > >> Due to dma-buf user map can't support direct I/O[1], the file read > >> must be buffer I/O. > >> > >> This means that during the process of reading the file into dma-buf, > >> page cache needs to be generated, and the corresponding content needs to > >> be first copied to the page cache before being copied to the dma-buf. > >> > >> This way worked well when reading relatively small files before, as > >> the page cache can cache the file content, thus improving performance. > >> > >> However, there are new challenges currently, especially as AI models are > >> becoming larger and need to be shared between DMA devices and the CPU > >> via dma-buf. > >> > >> For example, our 7B model file size is around 3.4GB. Using the > >> previous would mean generating a total of 3.4GB of page cache > >> (even if it will be reclaimed), and also requiring the copying of 3.4GB > >> of content between page cache and dma-buf. > >> > >> Due to the limited resources of system memory, files in the gigabyte > >> range > >> cannot persist in memory indefinitely, so this portion of page cache may > >> not provide much assistance for subsequent reads. Additionally, the > >> existence of page cache will consume additional system resources due to > >> the extra copying required by the CPU. > >> > >> Therefore, I think it is necessary for dma-buf to support direct I/O. > >> > >> However, direct I/O file reads cannot be performed using the buffer > >> mmaped by the user space for the dma-buf.[1] > >> > >> Here are some discussions on implementing direct I/O using dma-buf: > >> > >> mmap[1] > >> --- > >> dma-buf never support user map vaddr use of direct I/O. > >> > >> udmabuf[2] > >> --- > >> Currently, udmabuf can use the memfd method to read files into > >> dma-buf in direct I/O mode. > >> > >> However, if the size is large, the current udmabuf needs to adjust the > >> corresponding size_limit(default 64MB). > >> But using udmabuf for files at the 3GB level is not a very good > >> approach. > >> It needs to make some adjustments internally to handle this.[3] Or else, > >> fail create. > >> > >> But, it is indeed a viable way to enable dma-buf to support direct I/O. > >> However, it is necessary to initiate the file read after the memory > >> allocation > >> is completed, and handle race conditions carefully. > >> > >> sendfile/splice[4] > >> --- > >> Another way to enable dma-buf to support direct I/O is by implementing > >> splice_write/write_iter in the dma-buf file operations (fops) to adapt > >> to the sendfile method. > >> However, the current sendfile/splice calls are based on pipe. When using > >> direct I/O to read a file, the content needs to be copied to the buffer > >> allocated by the pipe (default 64KB), and then the dma-buf fops' > >> splice_write needs to be called to write the content into the dma-buf. > >> This approach requires serially reading the content of file pipe size > >> into the pipe buffer and then waiting for the dma-buf to be written > >> before reading the next one.(The I/O performance is relatively weak > >> under direct I/O.) > >> Moreover, due to the existence of the pipe buffer, even when using > >> direct I/O and not needing to generate additional page cache, > >> there still needs to be a CPU copy. > >> > >> copy_file_range[5] > >> --- > >> Consider of copy_file_range, It only supports copying files within the > >> same file system. Similarly, it is not very practical. > >> > >> > >> So, currently, there is no particularly suitable solution on VFS to > >> allow dma-buf to support direct I/O for large file reads. > >> > >> This patchset provides an idea to complete file reads when requesting a > >> dma-buf. > >> > >> Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag > >> === > >> This patch provides a method to immediately read the file content after > >> the dma-buf is allocated, and only returns the dma-buf file descriptor > >> after the file is fully read. > >> > >> Since the dma-buf file descriptor is not returned, no other thread can > >> access it except for the current thread, so we don't need to worry about > >> race conditions. > > > > That is a completely false assumption. > Can you provide a detailed explanation as to why this assumption is > incorrect? thanks. > > > >> > >> Map the dma-buf to the vmalloc area and initiate file reads in kernel > >> space, supporting both buffer I/O and direct I/O. > >> > >> This patch adds the DMA_HEAP_ALLOC_AND_READ heap_flag for user. > >> When a user needs to allocate a dma-buf and read a file, they should > >> pass this heap flag. As the size of the file being read is fixed, > >> there is no > >> need to pass the 'len' parameter. Instead, The file_fd needs to be > >> passed to > >> indicate to the kernel the file that needs to be read. > >> > >> The file open flag determines the mode of file reading. > >> But, please note that if direct I/O(O_DIRECT) is needed to read the > >> file, > >> the file size must be page aligned. (with patch 2-5, no need) > >> > >> Therefore, for the user, len and file_fd are mutually exclusive, > >> and they are combined using a union. > >> > >> Once the user obtains the dma-buf fd, the dma-buf directly contains the > >> file content. > > > > And I'm repeating myself, but this is a complete NAK from my side to > > this approach. > > > > We pointed out multiple ways of how to implement this cleanly and not > > by hacking functionality into the kernel which absolutely doesn't > > belong there. > In this patchset, I have provided performance comparisons of each of > these methods. Can you please provide more opinions? > > > > Regards, > > Christian. > > > >> > >> Patch 1 implement it. > >> > >> Patch 2-5 provides an approach for performance improvement. > >> > >> The DMA_HEAP_ALLOC_AND_READ_FILE heap flag patch enables us to > >> synchronously read files using direct I/O. > >> > >> This approach helps to save CPU copying and avoid a certain degree of > >> memory thrashing (page cache generation and reclamation) > >> > >> When dealing with large file sizes, the benefits of this approach become > >> particularly significant. > >> > >> However, there are currently some methods that can improve performance, > >> not just save system resources: > >> > >> Due to the large file size, for example, a AI 7B model of around > >> 3.4GB, the > >> time taken to allocate DMA-BUF memory will be relatively long. Waiting > >> for the allocation to complete before reading the file will add to the > >> overall time consumption. Therefore, the total time for DMA-BUF > >> allocation and file read can be calculated using the formula > >> T(total) = T(alloc) + T(I/O) > >> > >> However, if we change our approach, we don't necessarily need to wait > >> for the DMA-BUF allocation to complete before initiating I/O. In fact, > >> during the allocation process, we already hold a portion of the page, > >> which means that waiting for subsequent page allocations to complete > >> before carrying out file reads is actually unfair to the pages that have > >> already been allocated. > >> > >> The allocation of pages is sequential, and the reading of the file is > >> also sequential, with the content and size corresponding to the file. > >> This means that the memory location for each page, which holds the > >> content of a specific position in the file, can be determined at the > >> time of allocation. > >> > >> However, to fully leverage I/O performance, it is best to wait and > >> gather a certain number of pages before initiating batch processing. > >> > >> The default gather size is 128MB. So, ever gathered can see as a file > >> read > >> work, it maps the gather page to the vmalloc area to obtain a continuous > >> virtual address, which is used as a buffer to store the contents of the > >> corresponding file. So, if using direct I/O to read a file, the file > >> content will be written directly to the corresponding dma-buf buffer > >> memory > >> without any additional copying.(compare to pipe buffer.) > >> > >> Consider other ways to read into dma-buf. If we assume reading after > >> mmap > >> dma-buf, we need to map the pages of the dma-buf to the user virtual > >> address space. Also, udmabuf memfd need do this operations too. > >> Even if we support sendfile, the file copy also need buffer, you must > >> setup it. > >> So, mapping pages to the vmalloc area does not incur any additional > >> performance overhead compared to other methods.[6] > >> > >> Certainly, the administrator can also modify the gather size through > >> patch5. > >> > >> The formula for the time taken for system_heap buffer allocation and > >> file reading through async_read is as follows: > >> > >> T(total) = T(first gather page) + Max(T(remain alloc), T(I/O)) > >> > >> Compared to the synchronous read: > >> T(total) = T(alloc) + T(I/O) > >> > >> If the allocation time or I/O time is long, the time difference will be > >> covered by the maximum value between the allocation and I/O. The other > >> party will be concealed. > >> > >> Therefore, the larger the size of the file that needs to be read, the > >> greater the corresponding benefits will be. > >> > >> How to use > >> === > >> Consider the current pathway for loading model files into DMA-BUF: > >> 1. open dma-heap, get heap fd > >> 2. open file, get file_fd(can't use O_DIRECT) > >> 3. use file len to allocate dma-buf, get dma-buf fd > >> 4. mmap dma-buf fd, get vaddr > >> 5. read(file_fd, vaddr, file_size) into dma-buf pages > >> 6. share, attach, whatever you want > >> > >> Use DMA_HEAP_ALLOC_AND_READ_FILE JUST a little change: > >> 1. open dma-heap, get heap fd > >> 2. open file, get file_fd(buffer/direct) > >> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, > >> set file_fd > >> instead of len. get dma-buf fd(contains file content) > >> 4. share, attach, whatever you want > >> > >> So, test it is easy. > >> > >> How to test > >> === > >> The performance comparison will be conducted for the following > >> scenarios: > >> 1. normal > >> 2. udmabuf with [3] patch > >> 3. sendfile > >> 4. only patch 1 > >> 5. patch1 - patch4. > >> > >> normal: > >> 1. open dma-heap, get heap fd > >> 2. open file, get file_fd(can't use O_DIRECT) > >> 3. use file len to allocate dma-buf, get dma-buf fd > >> 4. mmap dma-buf fd, get vaddr > >> 5. read(file_fd, vaddr, file_size) into dma-buf pages > >> 6. share, attach, whatever you want > >> > >> UDMA-BUF step: > >> 1. memfd_create > >> 2. open file(buffer/direct) > >> 3. udmabuf create > >> 4. mmap memfd > >> 5. read file into memfd vaddr > >> > >> Sendfile step(need suit splice_write/write_iter, just use to compare): > >> 1. open dma-heap, get heap fd > >> 2. open file, get file_fd(buffer/direct) > >> 3. use file len to allocate dma-buf, get dma-buf fd > >> 4. sendfile file_fd to dma-buf fd > >> 6. share, attach, whatever you want > >> > >> patch1/patch1-4: > >> 1. open dma-heap, get heap fd > >> 2. open file, get file_fd(buffer/direct) > >> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, > >> set file_fd > >> instead of len. get dma-buf fd(contains file content) > >> 4. share, attach, whatever you want > >> > >> You can create a file to test it. Compare the performance gap between > >> the two. > >> It is best to compare the differences in file size from KB to MB to GB. > >> > >> The following test data will compare the performance differences > >> between 512KB, > >> 8MB, 1GB, and 3GB under various scenarios. > >> > >> Performance Test > >> === > >> 12G RAM phone > >> UFS4.0(the maximum speed is 4GB/s. ), > >> f2fs > >> kernel 6.1 with patch[7] (or else, can't support kvec direct I/O > >> read.) > >> no memory pressure. > >> drop_cache is used for each test. > >> > >> The average of 5 test results: > >> | scheme-size | 512KB(ns) | 8MB(ns) | 1GB(ns) | > >> 3GB(ns) | > >> | ------------------- | ---------- | ---------- | ------------- | > >> ------------- | > >> | normal | 2,790,861 | 14,535,784 | 1,520,790,492 | > >> 3,332,438,754 | > >> | udmabuf buffer I/O | 1,704,046 | 11,313,476 | 821,348,000 | > >> 2,108,419,923 | > >> | sendfile buffer I/O | 3,261,261 | 12,112,292 | 1,565,939,938 | > >> 3,062,052,984 | > >> | patch1-4 buffer I/O | 2,064,538 | 10,771,474 | 986,338,800 | > >> 2,187,570,861 | > >> | sendfile direct I/O | 12,844,231 | 37,883,938 | 5,110,299,184 | > >> 9,777,661,077 | > >> | patch1 direct I/O | 813,215 | 6,962,092 | 2,364,211,877 | > >> 5,648,897,554 | > >> | udmabuf direct I/O | 1,289,554 | 8,968,138 | 921,480,784 | > >> 2,158,305,738 | > >> | patch1-4 direct I/O | 1,957,661 | 6,581,999 | 520,003,538 | > >> 1,400,006,107 | > > With this test, sendfile can't give a good help base on pipe buffer. > > udmabuf is good, but I think our oem driver can't suit it. (And, AOSP do > not open this feature) Hi Huan, We should be able to turn on udmabuf for the Android kernels. We don't have CONFIG_UDMABUF because nobody has wanted it so far. It's encouraging to see your latest results! -T.J. > > Anyway, I am sending this patchset in the hope of further discussion. > > Thanks. > > >> > >> So, based on the test results: > >> > >> When the file is large, the patchset has the highest performance. > >> Compared to normal, patchset is a 50% improvement; > >> Compared to normal, patch1 only showed a degradation of 41%. > >> patch1 typical performance breakdown is as follows: > >> 1. alloc cost 188,802,693 ns > >> 2. vmap cost 42,491,385 ns > >> 3. file read cost 4,180,876,702 ns > >> Therefore, directly performing a single direct I/O read on a large file > >> may not be the most optimal way for performance. > >> > >> The performance of direct I/O implemented by the sendfile method is > >> the worst. > >> > >> When file size is small, The difference in performance is not > >> significant. This is consistent with expectations. > >> > >> > >> > >> Suggested use cases > >> === > >> 1. When there is a need to read large files and system resources > >> are scarce, > >> especially when the size of memory is limited.(GB level) In this > >> scenario, using direct I/O for file reading can even bring > >> performance > >> improvements.(may need patch2-3) > >> 2. For embedded devices with limited RAM, using direct I/O can > >> save system > >> resources and avoid unnecessary data copying. Therefore, even > >> if the > >> performance is lower when read small file, it can still be used > >> effectively. > >> 3. If there is sufficient memory, pinning the page cache of the > >> model files > >> in memory and placing file in the EROFS file system for > >> read-only access > >> maybe better.(EROFS do not support direct I/O) > >> > >> > >> Changlog > >> === > >> v1 [8] > >> v1->v2: > >> Uses the heap flag method for alloc and read instead of adding a new > >> DMA-buf ioctl command. [9] > >> Split the patchset to facilitate review and test. > >> patch 1 implement alloc and read, offer heap flag into it. > >> patch 2-4 offer async read > >> patch 5 can change gather limit. > >> > >> Reference > >> === > >> [1] > >> https://lore.kernel.org/all/0393cf47-3fa2-4e32-8b3d-d5d5bdece298@amd.com/ > >> [2] > >> https://lore.kernel.org/all/ZpTnzkdolpEwFbtu@phenom.ffwll.local/ > >> [3] > >> https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ > >> [4] > >> https://lore.kernel.org/all/Zpf5R7fRZZmEwVuR@infradead.org/ > >> [5] > >> https://lore.kernel.org/all/ZpiHKY2pGiBuEq4z@infradead.org/ > >> [6] > >> https://lore.kernel.org/all/9b70db2e-e562-4771-be6b-1fa8df19e356@amd.com/ > >> [7] > >> https://patchew.org/linux/20230209102954.528942-1-dhowells@redhat.com/20230… > >> [8] > >> https://lore.kernel.org/all/20240711074221.459589-1-link@vivo.com/ > >> [9] > >> https://lore.kernel.org/all/5ccbe705-883c-4651-9e66-6b452c414c74@amd.com/ > >> > >> Huan Yang (5): > >> dma-buf: heaps: Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag > >> dma-buf: heaps: Introduce async alloc read ops > >> dma-buf: heaps: support alloc async read file > >> dma-buf: heaps: system_heap alloc support async read > >> dma-buf: heaps: configurable async read gather limit > >> > >> drivers/dma-buf/dma-heap.c | 552 +++++++++++++++++++++++++++- > >> drivers/dma-buf/heaps/system_heap.c | 70 +++- > >> include/linux/dma-heap.h | 53 ++- > >> include/uapi/linux/dma-heap.h | 11 +- > >> 4 files changed, 673 insertions(+), 13 deletions(-) > >> > >> > >> base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890 > >

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Christian König

Am 30.07.24 um 13:36 schrieb Huan Yang: >>>> Either drop the whole approach or change udmabuf to do what you >>>> want to do. >>> OK, if so, do I need to send a patch to make dma-buf support sendfile? >> >> Well the udmabuf approach doesn't need to use sendfile, so no. > > Get it, I'll not send again. > > About udmabuf, I test find it can't support larget find read due to > page array alloc. > > I already upload this patch, but do not recive answer. > > https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ > > Is there anything wrong with my understanding of it? No, that patch was totally fine. Not getting a response is usually something good. In other words when maintainer see something which won't work at all they immediately react, but when nobody complains it usually means you are on the right track. As long as nobody has any good arguments against it I'm happy to take that one upstream through drm-misc-next immediately since it's clearly a stand a lone improvement on it's own. Regards, Christian. > >> >> Regards, >> Christian. >> >>> >>>> >>>> Apart from that I don't see a doable way which can be accepted into >>>> the kernel. >>> Thanks for your suggestion. >>>> >>>> Regards, >>>> Christian. >>>> >>>>>> >>>>>> Regards, >>>>>> Christian. >>>>>> >>>>>>> >>>>>>> Patch 1 implement it. >>>>>>> >>>>>>> Patch 2-5 provides an approach for performance improvement. >>>>>>> >>>>>>> The DMA_HEAP_ALLOC_AND_READ_FILE heap flag patch enables us to >>>>>>> synchronously read files using direct I/O. >>>>>>> >>>>>>> This approach helps to save CPU copying and avoid a certain >>>>>>> degree of >>>>>>> memory thrashing (page cache generation and reclamation) >>>>>>> >>>>>>> When dealing with large file sizes, the benefits of this >>>>>>> approach become >>>>>>> particularly significant. >>>>>>> >>>>>>> However, there are currently some methods that can improve >>>>>>> performance, >>>>>>> not just save system resources: >>>>>>> >>>>>>> Due to the large file size, for example, a AI 7B model of around >>>>>>> 3.4GB, the >>>>>>> time taken to allocate DMA-BUF memory will be relatively long. >>>>>>> Waiting >>>>>>> for the allocation to complete before reading the file will add >>>>>>> to the >>>>>>> overall time consumption. Therefore, the total time for DMA-BUF >>>>>>> allocation and file read can be calculated using the formula >>>>>>> T(total) = T(alloc) + T(I/O) >>>>>>> >>>>>>> However, if we change our approach, we don't necessarily need to >>>>>>> wait >>>>>>> for the DMA-BUF allocation to complete before initiating I/O. In >>>>>>> fact, >>>>>>> during the allocation process, we already hold a portion of the >>>>>>> page, >>>>>>> which means that waiting for subsequent page allocations to >>>>>>> complete >>>>>>> before carrying out file reads is actually unfair to the pages >>>>>>> that have >>>>>>> already been allocated. >>>>>>> >>>>>>> The allocation of pages is sequential, and the reading of the >>>>>>> file is >>>>>>> also sequential, with the content and size corresponding to the >>>>>>> file. >>>>>>> This means that the memory location for each page, which holds the >>>>>>> content of a specific position in the file, can be determined at >>>>>>> the >>>>>>> time of allocation. >>>>>>> >>>>>>> However, to fully leverage I/O performance, it is best to wait and >>>>>>> gather a certain number of pages before initiating batch >>>>>>> processing. >>>>>>> >>>>>>> The default gather size is 128MB. So, ever gathered can see as a >>>>>>> file read >>>>>>> work, it maps the gather page to the vmalloc area to obtain a >>>>>>> continuous >>>>>>> virtual address, which is used as a buffer to store the contents >>>>>>> of the >>>>>>> corresponding file. So, if using direct I/O to read a file, the >>>>>>> file >>>>>>> content will be written directly to the corresponding dma-buf >>>>>>> buffer memory >>>>>>> without any additional copying.(compare to pipe buffer.) >>>>>>> >>>>>>> Consider other ways to read into dma-buf. If we assume reading >>>>>>> after mmap >>>>>>> dma-buf, we need to map the pages of the dma-buf to the user >>>>>>> virtual >>>>>>> address space. Also, udmabuf memfd need do this operations too. >>>>>>> Even if we support sendfile, the file copy also need buffer, you >>>>>>> must >>>>>>> setup it. >>>>>>> So, mapping pages to the vmalloc area does not incur any additional >>>>>>> performance overhead compared to other methods.[6] >>>>>>> >>>>>>> Certainly, the administrator can also modify the gather size >>>>>>> through patch5. >>>>>>> >>>>>>> The formula for the time taken for system_heap buffer allocation >>>>>>> and >>>>>>> file reading through async_read is as follows: >>>>>>> >>>>>>> T(total) = T(first gather page) + Max(T(remain alloc), T(I/O)) >>>>>>> >>>>>>> Compared to the synchronous read: >>>>>>> T(total) = T(alloc) + T(I/O) >>>>>>> >>>>>>> If the allocation time or I/O time is long, the time difference >>>>>>> will be >>>>>>> covered by the maximum value between the allocation and I/O. The >>>>>>> other >>>>>>> party will be concealed. >>>>>>> >>>>>>> Therefore, the larger the size of the file that needs to be >>>>>>> read, the >>>>>>> greater the corresponding benefits will be. >>>>>>> >>>>>>> How to use >>>>>>> === >>>>>>> Consider the current pathway for loading model files into DMA-BUF: >>>>>>> 1. open dma-heap, get heap fd >>>>>>> 2. open file, get file_fd(can't use O_DIRECT) >>>>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>>>> 4. mmap dma-buf fd, get vaddr >>>>>>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>>>>>> 6. share, attach, whatever you want >>>>>>> >>>>>>> Use DMA_HEAP_ALLOC_AND_READ_FILE JUST a little change: >>>>>>> 1. open dma-heap, get heap fd >>>>>>> 2. open file, get file_fd(buffer/direct) >>>>>>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap >>>>>>> flag, set file_fd >>>>>>> instead of len. get dma-buf fd(contains file content) >>>>>>> 4. share, attach, whatever you want >>>>>>> >>>>>>> So, test it is easy. >>>>>>> >>>>>>> How to test >>>>>>> === >>>>>>> The performance comparison will be conducted for the following >>>>>>> scenarios: >>>>>>> 1. normal >>>>>>> 2. udmabuf with [3] patch >>>>>>> 3. sendfile >>>>>>> 4. only patch 1 >>>>>>> 5. patch1 - patch4. >>>>>>> >>>>>>> normal: >>>>>>> 1. open dma-heap, get heap fd >>>>>>> 2. open file, get file_fd(can't use O_DIRECT) >>>>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>>>> 4. mmap dma-buf fd, get vaddr >>>>>>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>>>>>> 6. share, attach, whatever you want >>>>>>> >>>>>>> UDMA-BUF step: >>>>>>> 1. memfd_create >>>>>>> 2. open file(buffer/direct) >>>>>>> 3. udmabuf create >>>>>>> 4. mmap memfd >>>>>>> 5. read file into memfd vaddr >>>>>>> >>>>>>> Sendfile step(need suit splice_write/write_iter, just use to >>>>>>> compare): >>>>>>> 1. open dma-heap, get heap fd >>>>>>> 2. open file, get file_fd(buffer/direct) >>>>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>>>> 4. sendfile file_fd to dma-buf fd >>>>>>> 6. share, attach, whatever you want >>>>>>> >>>>>>> patch1/patch1-4: >>>>>>> 1. open dma-heap, get heap fd >>>>>>> 2. open file, get file_fd(buffer/direct) >>>>>>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap >>>>>>> flag, set file_fd >>>>>>> instead of len. get dma-buf fd(contains file content) >>>>>>> 4. share, attach, whatever you want >>>>>>> >>>>>>> You can create a file to test it. Compare the performance gap >>>>>>> between the two. >>>>>>> It is best to compare the differences in file size from KB to MB >>>>>>> to GB. >>>>>>> >>>>>>> The following test data will compare the performance differences >>>>>>> between 512KB, >>>>>>> 8MB, 1GB, and 3GB under various scenarios. >>>>>>> >>>>>>> Performance Test >>>>>>> === >>>>>>> 12G RAM phone >>>>>>> UFS4.0(the maximum speed is 4GB/s. ), >>>>>>> f2fs >>>>>>> kernel 6.1 with patch[7] (or else, can't support kvec direct >>>>>>> I/O read.) >>>>>>> no memory pressure. >>>>>>> drop_cache is used for each test. >>>>>>> >>>>>>> The average of 5 test results: >>>>>>> | scheme-size | 512KB(ns) | 8MB(ns) | 1GB(ns) | >>>>>>> 3GB(ns) | >>>>>>> | ------------------- | ---------- | ---------- | ------------- >>>>>>> | ------------- | >>>>>>> | normal | 2,790,861 | 14,535,784 | 1,520,790,492 >>>>>>> | 3,332,438,754 | >>>>>>> | udmabuf buffer I/O | 1,704,046 | 11,313,476 | 821,348,000 | >>>>>>> 2,108,419,923 | >>>>>>> | sendfile buffer I/O | 3,261,261 | 12,112,292 | 1,565,939,938 >>>>>>> | 3,062,052,984 | >>>>>>> | patch1-4 buffer I/O | 2,064,538 | 10,771,474 | 986,338,800 | >>>>>>> 2,187,570,861 | >>>>>>> | sendfile direct I/O | 12,844,231 | 37,883,938 | 5,110,299,184 >>>>>>> | 9,777,661,077 | >>>>>>> | patch1 direct I/O | 813,215 | 6,962,092 | 2,364,211,877 >>>>>>> | 5,648,897,554 | >>>>>>> | udmabuf direct I/O | 1,289,554 | 8,968,138 | 921,480,784 | >>>>>>> 2,158,305,738 | >>>>>>> | patch1-4 direct I/O | 1,957,661 | 6,581,999 | 520,003,538 | >>>>>>> 1,400,006,107 | >>>>> >>>>> With this test, sendfile can't give a good help base on pipe buffer. >>>>> >>>>> udmabuf is good, but I think our oem driver can't suit it. (And, >>>>> AOSP do not open this feature) >>>>> >>>>> >>>>> Anyway, I am sending this patchset in the hope of further discussion. >>>>> >>>>> Thanks. >>>>> >>>>>>> >>>>>>> So, based on the test results: >>>>>>> >>>>>>> When the file is large, the patchset has the highest performance. >>>>>>> Compared to normal, patchset is a 50% improvement; >>>>>>> Compared to normal, patch1 only showed a degradation of 41%. >>>>>>> patch1 typical performance breakdown is as follows: >>>>>>> 1. alloc cost 188,802,693 ns >>>>>>> 2. vmap cost 42,491,385 ns >>>>>>> 3. file read cost 4,180,876,702 ns >>>>>>> Therefore, directly performing a single direct I/O read on a >>>>>>> large file >>>>>>> may not be the most optimal way for performance. >>>>>>> >>>>>>> The performance of direct I/O implemented by the sendfile method >>>>>>> is the worst. >>>>>>> >>>>>>> When file size is small, The difference in performance is not >>>>>>> significant. This is consistent with expectations. >>>>>>> >>>>>>> >>>>>>> >>>>>>> Suggested use cases >>>>>>> === >>>>>>> 1. When there is a need to read large files and system >>>>>>> resources are scarce, >>>>>>> especially when the size of memory is limited.(GB level) >>>>>>> In this >>>>>>> scenario, using direct I/O for file reading can even bring >>>>>>> performance >>>>>>> improvements.(may need patch2-3) >>>>>>> 2. For embedded devices with limited RAM, using direct I/O >>>>>>> can save system >>>>>>> resources and avoid unnecessary data copying. Therefore, >>>>>>> even if the >>>>>>> performance is lower when read small file, it can still be >>>>>>> used >>>>>>> effectively. >>>>>>> 3. If there is sufficient memory, pinning the page cache of >>>>>>> the model files >>>>>>> in memory and placing file in the EROFS file system for >>>>>>> read-only access >>>>>>> maybe better.(EROFS do not support direct I/O) >>>>>>> >>>>>>> >>>>>>> Changlog >>>>>>> === >>>>>>> v1 [8] >>>>>>> v1->v2: >>>>>>> Uses the heap flag method for alloc and read instead of >>>>>>> adding a new >>>>>>> DMA-buf ioctl command. [9] >>>>>>> Split the patchset to facilitate review and test. >>>>>>> patch 1 implement alloc and read, offer heap flag into it. >>>>>>> patch 2-4 offer async read >>>>>>> patch 5 can change gather limit. >>>>>>> >>>>>>> Reference >>>>>>> === >>>>>>> [1] >>>>>>> https://lore.kernel.org/all/0393cf47-3fa2-4e32-8b3d-d5d5bdece298@amd.com/ >>>>>>> [2] >>>>>>> https://lore.kernel.org/all/ZpTnzkdolpEwFbtu@phenom.ffwll.local/ >>>>>>> [3] >>>>>>> https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ >>>>>>> [4] https://lore.kernel.org/all/Zpf5R7fRZZmEwVuR@infradead.org/ >>>>>>> [5] https://lore.kernel.org/all/ZpiHKY2pGiBuEq4z@infradead.org/ >>>>>>> [6] >>>>>>> https://lore.kernel.org/all/9b70db2e-e562-4771-be6b-1fa8df19e356@amd.com/ >>>>>>> [7] >>>>>>> https://patchew.org/linux/20230209102954.528942-1-dhowells@redhat.com/20230… >>>>>>> [8] >>>>>>> https://lore.kernel.org/all/20240711074221.459589-1-link@vivo.com/ >>>>>>> [9] >>>>>>> https://lore.kernel.org/all/5ccbe705-883c-4651-9e66-6b452c414c74@amd.com/ >>>>>>> >>>>>>> Huan Yang (5): >>>>>>> dma-buf: heaps: Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag >>>>>>> dma-buf: heaps: Introduce async alloc read ops >>>>>>> dma-buf: heaps: support alloc async read file >>>>>>> dma-buf: heaps: system_heap alloc support async read >>>>>>> dma-buf: heaps: configurable async read gather limit >>>>>>> >>>>>>> drivers/dma-buf/dma-heap.c | 552 >>>>>>> +++++++++++++++++++++++++++- >>>>>>> drivers/dma-buf/heaps/system_heap.c | 70 +++- >>>>>>> include/linux/dma-heap.h | 53 ++- >>>>>>> include/uapi/linux/dma-heap.h | 11 +- >>>>>>> 4 files changed, 673 insertions(+), 13 deletions(-) >>>>>>> >>>>>>> >>>>>>> base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890 >>>>>> >>>> >>

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Christian König

Am 30.07.24 um 10:46 schrieb Huan Yang: > > 在 2024/7/30 16:37, Christian König 写道: >> Am 30.07.24 um 10:14 schrieb Huan Yang: >>> 在 2024/7/30 16:03, Christian König 写道: >>>> Am 30.07.24 um 09:57 schrieb Huan Yang: >>>>> Background >>>>> ==== >>>>> Some user may need load file into dma-buf, current way is: >>>>> 1. allocate a dma-buf, get dma-buf fd >>>>> 2. mmap dma-buf fd into user vaddr >>>>> 3. read(file_fd, vaddr, fsz) >>>>> Due to dma-buf user map can't support direct I/O[1], the file read >>>>> must be buffer I/O. >>>>> >>>>> This means that during the process of reading the file into dma-buf, >>>>> page cache needs to be generated, and the corresponding content >>>>> needs to >>>>> be first copied to the page cache before being copied to the dma-buf. >>>>> >>>>> This way worked well when reading relatively small files before, as >>>>> the page cache can cache the file content, thus improving >>>>> performance. >>>>> >>>>> However, there are new challenges currently, especially as AI >>>>> models are >>>>> becoming larger and need to be shared between DMA devices and the CPU >>>>> via dma-buf. >>>>> >>>>> For example, our 7B model file size is around 3.4GB. Using the >>>>> previous would mean generating a total of 3.4GB of page cache >>>>> (even if it will be reclaimed), and also requiring the copying of >>>>> 3.4GB >>>>> of content between page cache and dma-buf. >>>>> >>>>> Due to the limited resources of system memory, files in the >>>>> gigabyte range >>>>> cannot persist in memory indefinitely, so this portion of page >>>>> cache may >>>>> not provide much assistance for subsequent reads. Additionally, the >>>>> existence of page cache will consume additional system resources >>>>> due to >>>>> the extra copying required by the CPU. >>>>> >>>>> Therefore, I think it is necessary for dma-buf to support direct I/O. >>>>> >>>>> However, direct I/O file reads cannot be performed using the buffer >>>>> mmaped by the user space for the dma-buf.[1] >>>>> >>>>> Here are some discussions on implementing direct I/O using dma-buf: >>>>> >>>>> mmap[1] >>>>> --- >>>>> dma-buf never support user map vaddr use of direct I/O. >>>>> >>>>> udmabuf[2] >>>>> --- >>>>> Currently, udmabuf can use the memfd method to read files into >>>>> dma-buf in direct I/O mode. >>>>> >>>>> However, if the size is large, the current udmabuf needs to adjust >>>>> the >>>>> corresponding size_limit(default 64MB). >>>>> But using udmabuf for files at the 3GB level is not a very good >>>>> approach. >>>>> It needs to make some adjustments internally to handle this.[3] Or >>>>> else, >>>>> fail create. >>>>> >>>>> But, it is indeed a viable way to enable dma-buf to support direct >>>>> I/O. >>>>> However, it is necessary to initiate the file read after the >>>>> memory allocation >>>>> is completed, and handle race conditions carefully. >>>>> >>>>> sendfile/splice[4] >>>>> --- >>>>> Another way to enable dma-buf to support direct I/O is by >>>>> implementing >>>>> splice_write/write_iter in the dma-buf file operations (fops) to >>>>> adapt >>>>> to the sendfile method. >>>>> However, the current sendfile/splice calls are based on pipe. When >>>>> using >>>>> direct I/O to read a file, the content needs to be copied to the >>>>> buffer >>>>> allocated by the pipe (default 64KB), and then the dma-buf fops' >>>>> splice_write needs to be called to write the content into the >>>>> dma-buf. >>>>> This approach requires serially reading the content of file pipe size >>>>> into the pipe buffer and then waiting for the dma-buf to be written >>>>> before reading the next one.(The I/O performance is relatively weak >>>>> under direct I/O.) >>>>> Moreover, due to the existence of the pipe buffer, even when using >>>>> direct I/O and not needing to generate additional page cache, >>>>> there still needs to be a CPU copy. >>>>> >>>>> copy_file_range[5] >>>>> --- >>>>> Consider of copy_file_range, It only supports copying files within >>>>> the >>>>> same file system. Similarly, it is not very practical. >>>>> >>>>> >>>>> So, currently, there is no particularly suitable solution on VFS to >>>>> allow dma-buf to support direct I/O for large file reads. >>>>> >>>>> This patchset provides an idea to complete file reads when >>>>> requesting a >>>>> dma-buf. >>>>> >>>>> Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag >>>>> === >>>>> This patch provides a method to immediately read the file content >>>>> after >>>>> the dma-buf is allocated, and only returns the dma-buf file >>>>> descriptor >>>>> after the file is fully read. >>>>> >>>>> Since the dma-buf file descriptor is not returned, no other thread >>>>> can >>>>> access it except for the current thread, so we don't need to worry >>>>> about >>>>> race conditions. >>>> >>>> That is a completely false assumption. >>> Can you provide a detailed explanation as to why this assumption is >>> incorrect? thanks. >> >> File descriptors can be guessed and is available to userspace as soon >> as dma_buf_fd() is called. >> >> What could potentially work is to call system_heap_allocate() without >> calling dma_buf_fd(), but I'm not sure if you can then make I/O to >> the underlying pages. > > Actually, the dma-buf file descriptor is obtained only after a > successful file read in the code, so there is no issue. > > If you are interested, you can take a look at the > dma_heap_buffer_alloc_and_read function in patch1. > >> >>>> >>>>> >>>>> Map the dma-buf to the vmalloc area and initiate file reads in kernel >>>>> space, supporting both buffer I/O and direct I/O. >>>>> >>>>> This patch adds the DMA_HEAP_ALLOC_AND_READ heap_flag for user. >>>>> When a user needs to allocate a dma-buf and read a file, they should >>>>> pass this heap flag. As the size of the file being read is fixed, >>>>> there is no >>>>> need to pass the 'len' parameter. Instead, The file_fd needs to be >>>>> passed to >>>>> indicate to the kernel the file that needs to be read. >>>>> >>>>> The file open flag determines the mode of file reading. >>>>> But, please note that if direct I/O(O_DIRECT) is needed to read >>>>> the file, >>>>> the file size must be page aligned. (with patch 2-5, no need) >>>>> >>>>> Therefore, for the user, len and file_fd are mutually exclusive, >>>>> and they are combined using a union. >>>>> >>>>> Once the user obtains the dma-buf fd, the dma-buf directly >>>>> contains the >>>>> file content. >>>> >>>> And I'm repeating myself, but this is a complete NAK from my side >>>> to this approach. >>>> >>>> We pointed out multiple ways of how to implement this cleanly and >>>> not by hacking functionality into the kernel which absolutely >>>> doesn't belong there. >>> In this patchset, I have provided performance comparisons of each of >>> these methods. Can you please provide more opinions? >> >> Either drop the whole approach or change udmabuf to do what you want >> to do. > OK, if so, do I need to send a patch to make dma-buf support sendfile? Well the udmabuf approach doesn't need to use sendfile, so no. Regards, Christian. > >> >> Apart from that I don't see a doable way which can be accepted into >> the kernel. > Thanks for your suggestion. >> >> Regards, >> Christian. >> >>>> >>>> Regards, >>>> Christian. >>>> >>>>> >>>>> Patch 1 implement it. >>>>> >>>>> Patch 2-5 provides an approach for performance improvement. >>>>> >>>>> The DMA_HEAP_ALLOC_AND_READ_FILE heap flag patch enables us to >>>>> synchronously read files using direct I/O. >>>>> >>>>> This approach helps to save CPU copying and avoid a certain degree of >>>>> memory thrashing (page cache generation and reclamation) >>>>> >>>>> When dealing with large file sizes, the benefits of this approach >>>>> become >>>>> particularly significant. >>>>> >>>>> However, there are currently some methods that can improve >>>>> performance, >>>>> not just save system resources: >>>>> >>>>> Due to the large file size, for example, a AI 7B model of around >>>>> 3.4GB, the >>>>> time taken to allocate DMA-BUF memory will be relatively long. >>>>> Waiting >>>>> for the allocation to complete before reading the file will add to >>>>> the >>>>> overall time consumption. Therefore, the total time for DMA-BUF >>>>> allocation and file read can be calculated using the formula >>>>> T(total) = T(alloc) + T(I/O) >>>>> >>>>> However, if we change our approach, we don't necessarily need to wait >>>>> for the DMA-BUF allocation to complete before initiating I/O. In >>>>> fact, >>>>> during the allocation process, we already hold a portion of the page, >>>>> which means that waiting for subsequent page allocations to complete >>>>> before carrying out file reads is actually unfair to the pages >>>>> that have >>>>> already been allocated. >>>>> >>>>> The allocation of pages is sequential, and the reading of the file is >>>>> also sequential, with the content and size corresponding to the file. >>>>> This means that the memory location for each page, which holds the >>>>> content of a specific position in the file, can be determined at the >>>>> time of allocation. >>>>> >>>>> However, to fully leverage I/O performance, it is best to wait and >>>>> gather a certain number of pages before initiating batch processing. >>>>> >>>>> The default gather size is 128MB. So, ever gathered can see as a >>>>> file read >>>>> work, it maps the gather page to the vmalloc area to obtain a >>>>> continuous >>>>> virtual address, which is used as a buffer to store the contents >>>>> of the >>>>> corresponding file. So, if using direct I/O to read a file, the file >>>>> content will be written directly to the corresponding dma-buf >>>>> buffer memory >>>>> without any additional copying.(compare to pipe buffer.) >>>>> >>>>> Consider other ways to read into dma-buf. If we assume reading >>>>> after mmap >>>>> dma-buf, we need to map the pages of the dma-buf to the user virtual >>>>> address space. Also, udmabuf memfd need do this operations too. >>>>> Even if we support sendfile, the file copy also need buffer, you must >>>>> setup it. >>>>> So, mapping pages to the vmalloc area does not incur any additional >>>>> performance overhead compared to other methods.[6] >>>>> >>>>> Certainly, the administrator can also modify the gather size >>>>> through patch5. >>>>> >>>>> The formula for the time taken for system_heap buffer allocation and >>>>> file reading through async_read is as follows: >>>>> >>>>> T(total) = T(first gather page) + Max(T(remain alloc), T(I/O)) >>>>> >>>>> Compared to the synchronous read: >>>>> T(total) = T(alloc) + T(I/O) >>>>> >>>>> If the allocation time or I/O time is long, the time difference >>>>> will be >>>>> covered by the maximum value between the allocation and I/O. The >>>>> other >>>>> party will be concealed. >>>>> >>>>> Therefore, the larger the size of the file that needs to be read, the >>>>> greater the corresponding benefits will be. >>>>> >>>>> How to use >>>>> === >>>>> Consider the current pathway for loading model files into DMA-BUF: >>>>> 1. open dma-heap, get heap fd >>>>> 2. open file, get file_fd(can't use O_DIRECT) >>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>> 4. mmap dma-buf fd, get vaddr >>>>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>>>> 6. share, attach, whatever you want >>>>> >>>>> Use DMA_HEAP_ALLOC_AND_READ_FILE JUST a little change: >>>>> 1. open dma-heap, get heap fd >>>>> 2. open file, get file_fd(buffer/direct) >>>>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap >>>>> flag, set file_fd >>>>> instead of len. get dma-buf fd(contains file content) >>>>> 4. share, attach, whatever you want >>>>> >>>>> So, test it is easy. >>>>> >>>>> How to test >>>>> === >>>>> The performance comparison will be conducted for the following >>>>> scenarios: >>>>> 1. normal >>>>> 2. udmabuf with [3] patch >>>>> 3. sendfile >>>>> 4. only patch 1 >>>>> 5. patch1 - patch4. >>>>> >>>>> normal: >>>>> 1. open dma-heap, get heap fd >>>>> 2. open file, get file_fd(can't use O_DIRECT) >>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>> 4. mmap dma-buf fd, get vaddr >>>>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>>>> 6. share, attach, whatever you want >>>>> >>>>> UDMA-BUF step: >>>>> 1. memfd_create >>>>> 2. open file(buffer/direct) >>>>> 3. udmabuf create >>>>> 4. mmap memfd >>>>> 5. read file into memfd vaddr >>>>> >>>>> Sendfile step(need suit splice_write/write_iter, just use to >>>>> compare): >>>>> 1. open dma-heap, get heap fd >>>>> 2. open file, get file_fd(buffer/direct) >>>>> 3. use file len to allocate dma-buf, get dma-buf fd >>>>> 4. sendfile file_fd to dma-buf fd >>>>> 6. share, attach, whatever you want >>>>> >>>>> patch1/patch1-4: >>>>> 1. open dma-heap, get heap fd >>>>> 2. open file, get file_fd(buffer/direct) >>>>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap >>>>> flag, set file_fd >>>>> instead of len. get dma-buf fd(contains file content) >>>>> 4. share, attach, whatever you want >>>>> >>>>> You can create a file to test it. Compare the performance gap >>>>> between the two. >>>>> It is best to compare the differences in file size from KB to MB >>>>> to GB. >>>>> >>>>> The following test data will compare the performance differences >>>>> between 512KB, >>>>> 8MB, 1GB, and 3GB under various scenarios. >>>>> >>>>> Performance Test >>>>> === >>>>> 12G RAM phone >>>>> UFS4.0(the maximum speed is 4GB/s. ), >>>>> f2fs >>>>> kernel 6.1 with patch[7] (or else, can't support kvec direct >>>>> I/O read.) >>>>> no memory pressure. >>>>> drop_cache is used for each test. >>>>> >>>>> The average of 5 test results: >>>>> | scheme-size | 512KB(ns) | 8MB(ns) | 1GB(ns) | >>>>> 3GB(ns) | >>>>> | ------------------- | ---------- | ---------- | ------------- | >>>>> ------------- | >>>>> | normal | 2,790,861 | 14,535,784 | 1,520,790,492 | >>>>> 3,332,438,754 | >>>>> | udmabuf buffer I/O | 1,704,046 | 11,313,476 | 821,348,000 | >>>>> 2,108,419,923 | >>>>> | sendfile buffer I/O | 3,261,261 | 12,112,292 | 1,565,939,938 | >>>>> 3,062,052,984 | >>>>> | patch1-4 buffer I/O | 2,064,538 | 10,771,474 | 986,338,800 | >>>>> 2,187,570,861 | >>>>> | sendfile direct I/O | 12,844,231 | 37,883,938 | 5,110,299,184 | >>>>> 9,777,661,077 | >>>>> | patch1 direct I/O | 813,215 | 6,962,092 | 2,364,211,877 | >>>>> 5,648,897,554 | >>>>> | udmabuf direct I/O | 1,289,554 | 8,968,138 | 921,480,784 | >>>>> 2,158,305,738 | >>>>> | patch1-4 direct I/O | 1,957,661 | 6,581,999 | 520,003,538 | >>>>> 1,400,006,107 | >>> >>> With this test, sendfile can't give a good help base on pipe buffer. >>> >>> udmabuf is good, but I think our oem driver can't suit it. (And, >>> AOSP do not open this feature) >>> >>> >>> Anyway, I am sending this patchset in the hope of further discussion. >>> >>> Thanks. >>> >>>>> >>>>> So, based on the test results: >>>>> >>>>> When the file is large, the patchset has the highest performance. >>>>> Compared to normal, patchset is a 50% improvement; >>>>> Compared to normal, patch1 only showed a degradation of 41%. >>>>> patch1 typical performance breakdown is as follows: >>>>> 1. alloc cost 188,802,693 ns >>>>> 2. vmap cost 42,491,385 ns >>>>> 3. file read cost 4,180,876,702 ns >>>>> Therefore, directly performing a single direct I/O read on a large >>>>> file >>>>> may not be the most optimal way for performance. >>>>> >>>>> The performance of direct I/O implemented by the sendfile method >>>>> is the worst. >>>>> >>>>> When file size is small, The difference in performance is not >>>>> significant. This is consistent with expectations. >>>>> >>>>> >>>>> >>>>> Suggested use cases >>>>> === >>>>> 1. When there is a need to read large files and system >>>>> resources are scarce, >>>>> especially when the size of memory is limited.(GB level) In >>>>> this >>>>> scenario, using direct I/O for file reading can even bring >>>>> performance >>>>> improvements.(may need patch2-3) >>>>> 2. For embedded devices with limited RAM, using direct I/O can >>>>> save system >>>>> resources and avoid unnecessary data copying. Therefore, >>>>> even if the >>>>> performance is lower when read small file, it can still be used >>>>> effectively. >>>>> 3. If there is sufficient memory, pinning the page cache of the >>>>> model files >>>>> in memory and placing file in the EROFS file system for >>>>> read-only access >>>>> maybe better.(EROFS do not support direct I/O) >>>>> >>>>> >>>>> Changlog >>>>> === >>>>> v1 [8] >>>>> v1->v2: >>>>> Uses the heap flag method for alloc and read instead of adding >>>>> a new >>>>> DMA-buf ioctl command. [9] >>>>> Split the patchset to facilitate review and test. >>>>> patch 1 implement alloc and read, offer heap flag into it. >>>>> patch 2-4 offer async read >>>>> patch 5 can change gather limit. >>>>> >>>>> Reference >>>>> === >>>>> [1] >>>>> https://lore.kernel.org/all/0393cf47-3fa2-4e32-8b3d-d5d5bdece298@amd.com/ >>>>> [2] https://lore.kernel.org/all/ZpTnzkdolpEwFbtu@phenom.ffwll.local/ >>>>> [3] >>>>> https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ >>>>> [4] https://lore.kernel.org/all/Zpf5R7fRZZmEwVuR@infradead.org/ >>>>> [5] https://lore.kernel.org/all/ZpiHKY2pGiBuEq4z@infradead.org/ >>>>> [6] >>>>> https://lore.kernel.org/all/9b70db2e-e562-4771-be6b-1fa8df19e356@amd.com/ >>>>> [7] >>>>> https://patchew.org/linux/20230209102954.528942-1-dhowells@redhat.com/20230… >>>>> [8] >>>>> https://lore.kernel.org/all/20240711074221.459589-1-link@vivo.com/ >>>>> [9] >>>>> https://lore.kernel.org/all/5ccbe705-883c-4651-9e66-6b452c414c74@amd.com/ >>>>> >>>>> Huan Yang (5): >>>>> dma-buf: heaps: Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag >>>>> dma-buf: heaps: Introduce async alloc read ops >>>>> dma-buf: heaps: support alloc async read file >>>>> dma-buf: heaps: system_heap alloc support async read >>>>> dma-buf: heaps: configurable async read gather limit >>>>> >>>>> drivers/dma-buf/dma-heap.c | 552 >>>>> +++++++++++++++++++++++++++- >>>>> drivers/dma-buf/heaps/system_heap.c | 70 +++- >>>>> include/linux/dma-heap.h | 53 ++- >>>>> include/uapi/linux/dma-heap.h | 11 +- >>>>> 4 files changed, 673 insertions(+), 13 deletions(-) >>>>> >>>>> >>>>> base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890 >>>> >>

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Christian König

Am 30.07.24 um 11:05 schrieb Huan Yang: > > 在 2024/7/30 16:56, Daniel Vetter 写道: >> [????????? daniel.vetter(a)ffwll.ch ????????? >> https://aka.ms/LearnAboutSenderIdentification?????????????] >> >> On Tue, Jul 30, 2024 at 03:57:44PM +0800, Huan Yang wrote: >>> UDMA-BUF step: >>> 1. memfd_create >>> 2. open file(buffer/direct) >>> 3. udmabuf create >>> 4. mmap memfd >>> 5. read file into memfd vaddr >> Yeah this is really slow and the worst way to do it. You absolutely want >> to start _all_ the io before you start creating the dma-buf, ideally >> with >> everything running in parallel. But just starting the direct I/O with >> async and then creating the umdabuf should be a lot faster and avoid > That's greate, Let me rephrase that, and please correct me if I'm wrong. > > UDMA-BUF step: > 1. memfd_create > 2. mmap memfd > 3. open file(buffer/direct) > 4. start thread to async read > 3. udmabuf create > > With this, can improve > >> needlessly serialization operations. >> >> The other issue is that the mmap has some overhead, but might not be too >> bad. > Yes, the time spent on page fault in mmap should be negligible > compared to the time spent on file read. You should try to avoid mmap as much as possible. Especially the TLB invalidation overhead is really huge on platforms with a large number of CPUs. Regards, Christian. >> -Sima >> -- >> Daniel Vetter >> Software Engineer, Intel Corporation >> http://blog.ffwll.ch

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Daniel Vetter

On Tue, Jul 30, 2024 at 03:57:44PM +0800, Huan Yang wrote: > UDMA-BUF step: > 1. memfd_create > 2. open file(buffer/direct) > 3. udmabuf create > 4. mmap memfd > 5. read file into memfd vaddr Yeah this is really slow and the worst way to do it. You absolutely want to start _all_ the io before you start creating the dma-buf, ideally with everything running in parallel. But just starting the direct I/O with async and then creating the umdabuf should be a lot faster and avoid needlessly serialization operations. The other issue is that the mmap has some overhead, but might not be too bad. -Sima -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch

2 years, 3 months

Re: [PATCH] MAINTAINERS: Add selftests to DMA-BUF HEAPS FRAMEWORK entry

by Daniel Vetter

On Mon, Jul 29, 2024 at 04:12:02PM +0800, Zenghui Yu wrote: > Include dmabuf-heaps selftests in the correct entry so that updates to it > can be sent to the right place. > > Signed-off-by: Zenghui Yu <yuzenghui(a)huawei.com> Applied to drm-misc-next, thanks for your patch. -Sima > --- > MAINTAINERS | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/MAINTAINERS b/MAINTAINERS > index 42decde38320..b7f24c9fb0e2 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -6660,6 +6660,7 @@ F: drivers/dma-buf/dma-heap.c > F: drivers/dma-buf/heaps/* > F: include/linux/dma-heap.h > F: include/uapi/linux/dma-heap.h > +F: tools/testing/selftests/dmabuf-heaps/ > > DMC FREQUENCY DRIVER FOR SAMSUNG EXYNOS5422 > M: Lukasz Luba <lukasz.luba(a)arm.com> > -- > 2.33.0 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Christian König

Am 30.07.24 um 10:14 schrieb Huan Yang: > 在 2024/7/30 16:03, Christian König 写道: >> Am 30.07.24 um 09:57 schrieb Huan Yang: >>> Background >>> ==== >>> Some user may need load file into dma-buf, current way is: >>> 1. allocate a dma-buf, get dma-buf fd >>> 2. mmap dma-buf fd into user vaddr >>> 3. read(file_fd, vaddr, fsz) >>> Due to dma-buf user map can't support direct I/O[1], the file read >>> must be buffer I/O. >>> >>> This means that during the process of reading the file into dma-buf, >>> page cache needs to be generated, and the corresponding content >>> needs to >>> be first copied to the page cache before being copied to the dma-buf. >>> >>> This way worked well when reading relatively small files before, as >>> the page cache can cache the file content, thus improving performance. >>> >>> However, there are new challenges currently, especially as AI models >>> are >>> becoming larger and need to be shared between DMA devices and the CPU >>> via dma-buf. >>> >>> For example, our 7B model file size is around 3.4GB. Using the >>> previous would mean generating a total of 3.4GB of page cache >>> (even if it will be reclaimed), and also requiring the copying of 3.4GB >>> of content between page cache and dma-buf. >>> >>> Due to the limited resources of system memory, files in the gigabyte >>> range >>> cannot persist in memory indefinitely, so this portion of page cache >>> may >>> not provide much assistance for subsequent reads. Additionally, the >>> existence of page cache will consume additional system resources due to >>> the extra copying required by the CPU. >>> >>> Therefore, I think it is necessary for dma-buf to support direct I/O. >>> >>> However, direct I/O file reads cannot be performed using the buffer >>> mmaped by the user space for the dma-buf.[1] >>> >>> Here are some discussions on implementing direct I/O using dma-buf: >>> >>> mmap[1] >>> --- >>> dma-buf never support user map vaddr use of direct I/O. >>> >>> udmabuf[2] >>> --- >>> Currently, udmabuf can use the memfd method to read files into >>> dma-buf in direct I/O mode. >>> >>> However, if the size is large, the current udmabuf needs to adjust the >>> corresponding size_limit(default 64MB). >>> But using udmabuf for files at the 3GB level is not a very good >>> approach. >>> It needs to make some adjustments internally to handle this.[3] Or >>> else, >>> fail create. >>> >>> But, it is indeed a viable way to enable dma-buf to support direct I/O. >>> However, it is necessary to initiate the file read after the memory >>> allocation >>> is completed, and handle race conditions carefully. >>> >>> sendfile/splice[4] >>> --- >>> Another way to enable dma-buf to support direct I/O is by implementing >>> splice_write/write_iter in the dma-buf file operations (fops) to adapt >>> to the sendfile method. >>> However, the current sendfile/splice calls are based on pipe. When >>> using >>> direct I/O to read a file, the content needs to be copied to the buffer >>> allocated by the pipe (default 64KB), and then the dma-buf fops' >>> splice_write needs to be called to write the content into the dma-buf. >>> This approach requires serially reading the content of file pipe size >>> into the pipe buffer and then waiting for the dma-buf to be written >>> before reading the next one.(The I/O performance is relatively weak >>> under direct I/O.) >>> Moreover, due to the existence of the pipe buffer, even when using >>> direct I/O and not needing to generate additional page cache, >>> there still needs to be a CPU copy. >>> >>> copy_file_range[5] >>> --- >>> Consider of copy_file_range, It only supports copying files within the >>> same file system. Similarly, it is not very practical. >>> >>> >>> So, currently, there is no particularly suitable solution on VFS to >>> allow dma-buf to support direct I/O for large file reads. >>> >>> This patchset provides an idea to complete file reads when requesting a >>> dma-buf. >>> >>> Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag >>> === >>> This patch provides a method to immediately read the file content after >>> the dma-buf is allocated, and only returns the dma-buf file descriptor >>> after the file is fully read. >>> >>> Since the dma-buf file descriptor is not returned, no other thread can >>> access it except for the current thread, so we don't need to worry >>> about >>> race conditions. >> >> That is a completely false assumption. > Can you provide a detailed explanation as to why this assumption is > incorrect? thanks. File descriptors can be guessed and is available to userspace as soon as dma_buf_fd() is called. What could potentially work is to call system_heap_allocate() without calling dma_buf_fd(), but I'm not sure if you can then make I/O to the underlying pages. >> >>> >>> Map the dma-buf to the vmalloc area and initiate file reads in kernel >>> space, supporting both buffer I/O and direct I/O. >>> >>> This patch adds the DMA_HEAP_ALLOC_AND_READ heap_flag for user. >>> When a user needs to allocate a dma-buf and read a file, they should >>> pass this heap flag. As the size of the file being read is fixed, >>> there is no >>> need to pass the 'len' parameter. Instead, The file_fd needs to be >>> passed to >>> indicate to the kernel the file that needs to be read. >>> >>> The file open flag determines the mode of file reading. >>> But, please note that if direct I/O(O_DIRECT) is needed to read the >>> file, >>> the file size must be page aligned. (with patch 2-5, no need) >>> >>> Therefore, for the user, len and file_fd are mutually exclusive, >>> and they are combined using a union. >>> >>> Once the user obtains the dma-buf fd, the dma-buf directly contains the >>> file content. >> >> And I'm repeating myself, but this is a complete NAK from my side to >> this approach. >> >> We pointed out multiple ways of how to implement this cleanly and not >> by hacking functionality into the kernel which absolutely doesn't >> belong there. > In this patchset, I have provided performance comparisons of each of > these methods. Can you please provide more opinions? Either drop the whole approach or change udmabuf to do what you want to do. Apart from that I don't see a doable way which can be accepted into the kernel. Regards, Christian. >> >> Regards, >> Christian. >> >>> >>> Patch 1 implement it. >>> >>> Patch 2-5 provides an approach for performance improvement. >>> >>> The DMA_HEAP_ALLOC_AND_READ_FILE heap flag patch enables us to >>> synchronously read files using direct I/O. >>> >>> This approach helps to save CPU copying and avoid a certain degree of >>> memory thrashing (page cache generation and reclamation) >>> >>> When dealing with large file sizes, the benefits of this approach >>> become >>> particularly significant. >>> >>> However, there are currently some methods that can improve performance, >>> not just save system resources: >>> >>> Due to the large file size, for example, a AI 7B model of around >>> 3.4GB, the >>> time taken to allocate DMA-BUF memory will be relatively long. Waiting >>> for the allocation to complete before reading the file will add to the >>> overall time consumption. Therefore, the total time for DMA-BUF >>> allocation and file read can be calculated using the formula >>> T(total) = T(alloc) + T(I/O) >>> >>> However, if we change our approach, we don't necessarily need to wait >>> for the DMA-BUF allocation to complete before initiating I/O. In fact, >>> during the allocation process, we already hold a portion of the page, >>> which means that waiting for subsequent page allocations to complete >>> before carrying out file reads is actually unfair to the pages that >>> have >>> already been allocated. >>> >>> The allocation of pages is sequential, and the reading of the file is >>> also sequential, with the content and size corresponding to the file. >>> This means that the memory location for each page, which holds the >>> content of a specific position in the file, can be determined at the >>> time of allocation. >>> >>> However, to fully leverage I/O performance, it is best to wait and >>> gather a certain number of pages before initiating batch processing. >>> >>> The default gather size is 128MB. So, ever gathered can see as a >>> file read >>> work, it maps the gather page to the vmalloc area to obtain a >>> continuous >>> virtual address, which is used as a buffer to store the contents of the >>> corresponding file. So, if using direct I/O to read a file, the file >>> content will be written directly to the corresponding dma-buf buffer >>> memory >>> without any additional copying.(compare to pipe buffer.) >>> >>> Consider other ways to read into dma-buf. If we assume reading after >>> mmap >>> dma-buf, we need to map the pages of the dma-buf to the user virtual >>> address space. Also, udmabuf memfd need do this operations too. >>> Even if we support sendfile, the file copy also need buffer, you must >>> setup it. >>> So, mapping pages to the vmalloc area does not incur any additional >>> performance overhead compared to other methods.[6] >>> >>> Certainly, the administrator can also modify the gather size through >>> patch5. >>> >>> The formula for the time taken for system_heap buffer allocation and >>> file reading through async_read is as follows: >>> >>> T(total) = T(first gather page) + Max(T(remain alloc), T(I/O)) >>> >>> Compared to the synchronous read: >>> T(total) = T(alloc) + T(I/O) >>> >>> If the allocation time or I/O time is long, the time difference will be >>> covered by the maximum value between the allocation and I/O. The other >>> party will be concealed. >>> >>> Therefore, the larger the size of the file that needs to be read, the >>> greater the corresponding benefits will be. >>> >>> How to use >>> === >>> Consider the current pathway for loading model files into DMA-BUF: >>> 1. open dma-heap, get heap fd >>> 2. open file, get file_fd(can't use O_DIRECT) >>> 3. use file len to allocate dma-buf, get dma-buf fd >>> 4. mmap dma-buf fd, get vaddr >>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>> 6. share, attach, whatever you want >>> >>> Use DMA_HEAP_ALLOC_AND_READ_FILE JUST a little change: >>> 1. open dma-heap, get heap fd >>> 2. open file, get file_fd(buffer/direct) >>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, >>> set file_fd >>> instead of len. get dma-buf fd(contains file content) >>> 4. share, attach, whatever you want >>> >>> So, test it is easy. >>> >>> How to test >>> === >>> The performance comparison will be conducted for the following >>> scenarios: >>> 1. normal >>> 2. udmabuf with [3] patch >>> 3. sendfile >>> 4. only patch 1 >>> 5. patch1 - patch4. >>> >>> normal: >>> 1. open dma-heap, get heap fd >>> 2. open file, get file_fd(can't use O_DIRECT) >>> 3. use file len to allocate dma-buf, get dma-buf fd >>> 4. mmap dma-buf fd, get vaddr >>> 5. read(file_fd, vaddr, file_size) into dma-buf pages >>> 6. share, attach, whatever you want >>> >>> UDMA-BUF step: >>> 1. memfd_create >>> 2. open file(buffer/direct) >>> 3. udmabuf create >>> 4. mmap memfd >>> 5. read file into memfd vaddr >>> >>> Sendfile step(need suit splice_write/write_iter, just use to compare): >>> 1. open dma-heap, get heap fd >>> 2. open file, get file_fd(buffer/direct) >>> 3. use file len to allocate dma-buf, get dma-buf fd >>> 4. sendfile file_fd to dma-buf fd >>> 6. share, attach, whatever you want >>> >>> patch1/patch1-4: >>> 1. open dma-heap, get heap fd >>> 2. open file, get file_fd(buffer/direct) >>> 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, >>> set file_fd >>> instead of len. get dma-buf fd(contains file content) >>> 4. share, attach, whatever you want >>> >>> You can create a file to test it. Compare the performance gap >>> between the two. >>> It is best to compare the differences in file size from KB to MB to GB. >>> >>> The following test data will compare the performance differences >>> between 512KB, >>> 8MB, 1GB, and 3GB under various scenarios. >>> >>> Performance Test >>> === >>> 12G RAM phone >>> UFS4.0(the maximum speed is 4GB/s. ), >>> f2fs >>> kernel 6.1 with patch[7] (or else, can't support kvec direct I/O >>> read.) >>> no memory pressure. >>> drop_cache is used for each test. >>> >>> The average of 5 test results: >>> | scheme-size | 512KB(ns) | 8MB(ns) | 1GB(ns) | >>> 3GB(ns) | >>> | ------------------- | ---------- | ---------- | ------------- | >>> ------------- | >>> | normal | 2,790,861 | 14,535,784 | 1,520,790,492 | >>> 3,332,438,754 | >>> | udmabuf buffer I/O | 1,704,046 | 11,313,476 | 821,348,000 | >>> 2,108,419,923 | >>> | sendfile buffer I/O | 3,261,261 | 12,112,292 | 1,565,939,938 | >>> 3,062,052,984 | >>> | patch1-4 buffer I/O | 2,064,538 | 10,771,474 | 986,338,800 | >>> 2,187,570,861 | >>> | sendfile direct I/O | 12,844,231 | 37,883,938 | 5,110,299,184 | >>> 9,777,661,077 | >>> | patch1 direct I/O | 813,215 | 6,962,092 | 2,364,211,877 | >>> 5,648,897,554 | >>> | udmabuf direct I/O | 1,289,554 | 8,968,138 | 921,480,784 | >>> 2,158,305,738 | >>> | patch1-4 direct I/O | 1,957,661 | 6,581,999 | 520,003,538 | >>> 1,400,006,107 | > > With this test, sendfile can't give a good help base on pipe buffer. > > udmabuf is good, but I think our oem driver can't suit it. (And, AOSP > do not open this feature) > > > Anyway, I am sending this patchset in the hope of further discussion. > > Thanks. > >>> >>> So, based on the test results: >>> >>> When the file is large, the patchset has the highest performance. >>> Compared to normal, patchset is a 50% improvement; >>> Compared to normal, patch1 only showed a degradation of 41%. >>> patch1 typical performance breakdown is as follows: >>> 1. alloc cost 188,802,693 ns >>> 2. vmap cost 42,491,385 ns >>> 3. file read cost 4,180,876,702 ns >>> Therefore, directly performing a single direct I/O read on a large file >>> may not be the most optimal way for performance. >>> >>> The performance of direct I/O implemented by the sendfile method is >>> the worst. >>> >>> When file size is small, The difference in performance is not >>> significant. This is consistent with expectations. >>> >>> >>> >>> Suggested use cases >>> === >>> 1. When there is a need to read large files and system resources >>> are scarce, >>> especially when the size of memory is limited.(GB level) In this >>> scenario, using direct I/O for file reading can even bring >>> performance >>> improvements.(may need patch2-3) >>> 2. For embedded devices with limited RAM, using direct I/O can >>> save system >>> resources and avoid unnecessary data copying. Therefore, even >>> if the >>> performance is lower when read small file, it can still be used >>> effectively. >>> 3. If there is sufficient memory, pinning the page cache of the >>> model files >>> in memory and placing file in the EROFS file system for >>> read-only access >>> maybe better.(EROFS do not support direct I/O) >>> >>> >>> Changlog >>> === >>> v1 [8] >>> v1->v2: >>> Uses the heap flag method for alloc and read instead of adding a >>> new >>> DMA-buf ioctl command. [9] >>> Split the patchset to facilitate review and test. >>> patch 1 implement alloc and read, offer heap flag into it. >>> patch 2-4 offer async read >>> patch 5 can change gather limit. >>> >>> Reference >>> === >>> [1] >>> https://lore.kernel.org/all/0393cf47-3fa2-4e32-8b3d-d5d5bdece298@amd.com/ >>> [2] https://lore.kernel.org/all/ZpTnzkdolpEwFbtu@phenom.ffwll.local/ >>> [3] https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ >>> [4] https://lore.kernel.org/all/Zpf5R7fRZZmEwVuR@infradead.org/ >>> [5] https://lore.kernel.org/all/ZpiHKY2pGiBuEq4z@infradead.org/ >>> [6] >>> https://lore.kernel.org/all/9b70db2e-e562-4771-be6b-1fa8df19e356@amd.com/ >>> [7] >>> https://patchew.org/linux/20230209102954.528942-1-dhowells@redhat.com/20230… >>> [8] https://lore.kernel.org/all/20240711074221.459589-1-link@vivo.com/ >>> [9] >>> https://lore.kernel.org/all/5ccbe705-883c-4651-9e66-6b452c414c74@amd.com/ >>> >>> Huan Yang (5): >>> dma-buf: heaps: Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag >>> dma-buf: heaps: Introduce async alloc read ops >>> dma-buf: heaps: support alloc async read file >>> dma-buf: heaps: system_heap alloc support async read >>> dma-buf: heaps: configurable async read gather limit >>> >>> drivers/dma-buf/dma-heap.c | 552 >>> +++++++++++++++++++++++++++- >>> drivers/dma-buf/heaps/system_heap.c | 70 +++- >>> include/linux/dma-heap.h | 53 ++- >>> include/uapi/linux/dma-heap.h | 11 +- >>> 4 files changed, 673 insertions(+), 13 deletions(-) >>> >>> >>> base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890 >>

2 years, 3 months

Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

by Christian König

Am 30.07.24 um 09:57 schrieb Huan Yang: > Background > ==== > Some user may need load file into dma-buf, current way is: > 1. allocate a dma-buf, get dma-buf fd > 2. mmap dma-buf fd into user vaddr > 3. read(file_fd, vaddr, fsz) > Due to dma-buf user map can't support direct I/O[1], the file read > must be buffer I/O. > > This means that during the process of reading the file into dma-buf, > page cache needs to be generated, and the corresponding content needs to > be first copied to the page cache before being copied to the dma-buf. > > This way worked well when reading relatively small files before, as > the page cache can cache the file content, thus improving performance. > > However, there are new challenges currently, especially as AI models are > becoming larger and need to be shared between DMA devices and the CPU > via dma-buf. > > For example, our 7B model file size is around 3.4GB. Using the > previous would mean generating a total of 3.4GB of page cache > (even if it will be reclaimed), and also requiring the copying of 3.4GB > of content between page cache and dma-buf. > > Due to the limited resources of system memory, files in the gigabyte range > cannot persist in memory indefinitely, so this portion of page cache may > not provide much assistance for subsequent reads. Additionally, the > existence of page cache will consume additional system resources due to > the extra copying required by the CPU. > > Therefore, I think it is necessary for dma-buf to support direct I/O. > > However, direct I/O file reads cannot be performed using the buffer > mmaped by the user space for the dma-buf.[1] > > Here are some discussions on implementing direct I/O using dma-buf: > > mmap[1] > --- > dma-buf never support user map vaddr use of direct I/O. > > udmabuf[2] > --- > Currently, udmabuf can use the memfd method to read files into > dma-buf in direct I/O mode. > > However, if the size is large, the current udmabuf needs to adjust the > corresponding size_limit(default 64MB). > But using udmabuf for files at the 3GB level is not a very good approach. > It needs to make some adjustments internally to handle this.[3] Or else, > fail create. > > But, it is indeed a viable way to enable dma-buf to support direct I/O. > However, it is necessary to initiate the file read after the memory allocation > is completed, and handle race conditions carefully. > > sendfile/splice[4] > --- > Another way to enable dma-buf to support direct I/O is by implementing > splice_write/write_iter in the dma-buf file operations (fops) to adapt > to the sendfile method. > However, the current sendfile/splice calls are based on pipe. When using > direct I/O to read a file, the content needs to be copied to the buffer > allocated by the pipe (default 64KB), and then the dma-buf fops' > splice_write needs to be called to write the content into the dma-buf. > This approach requires serially reading the content of file pipe size > into the pipe buffer and then waiting for the dma-buf to be written > before reading the next one.(The I/O performance is relatively weak > under direct I/O.) > Moreover, due to the existence of the pipe buffer, even when using > direct I/O and not needing to generate additional page cache, > there still needs to be a CPU copy. > > copy_file_range[5] > --- > Consider of copy_file_range, It only supports copying files within the > same file system. Similarly, it is not very practical. > > > So, currently, there is no particularly suitable solution on VFS to > allow dma-buf to support direct I/O for large file reads. > > This patchset provides an idea to complete file reads when requesting a > dma-buf. > > Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag > === > This patch provides a method to immediately read the file content after > the dma-buf is allocated, and only returns the dma-buf file descriptor > after the file is fully read. > > Since the dma-buf file descriptor is not returned, no other thread can > access it except for the current thread, so we don't need to worry about > race conditions. That is a completely false assumption. > > Map the dma-buf to the vmalloc area and initiate file reads in kernel > space, supporting both buffer I/O and direct I/O. > > This patch adds the DMA_HEAP_ALLOC_AND_READ heap_flag for user. > When a user needs to allocate a dma-buf and read a file, they should > pass this heap flag. As the size of the file being read is fixed, there is no > need to pass the 'len' parameter. Instead, The file_fd needs to be passed to > indicate to the kernel the file that needs to be read. > > The file open flag determines the mode of file reading. > But, please note that if direct I/O(O_DIRECT) is needed to read the file, > the file size must be page aligned. (with patch 2-5, no need) > > Therefore, for the user, len and file_fd are mutually exclusive, > and they are combined using a union. > > Once the user obtains the dma-buf fd, the dma-buf directly contains the > file content. And I'm repeating myself, but this is a complete NAK from my side to this approach. We pointed out multiple ways of how to implement this cleanly and not by hacking functionality into the kernel which absolutely doesn't belong there. Regards, Christian. > > Patch 1 implement it. > > Patch 2-5 provides an approach for performance improvement. > > The DMA_HEAP_ALLOC_AND_READ_FILE heap flag patch enables us to > synchronously read files using direct I/O. > > This approach helps to save CPU copying and avoid a certain degree of > memory thrashing (page cache generation and reclamation) > > When dealing with large file sizes, the benefits of this approach become > particularly significant. > > However, there are currently some methods that can improve performance, > not just save system resources: > > Due to the large file size, for example, a AI 7B model of around 3.4GB, the > time taken to allocate DMA-BUF memory will be relatively long. Waiting > for the allocation to complete before reading the file will add to the > overall time consumption. Therefore, the total time for DMA-BUF > allocation and file read can be calculated using the formula > T(total) = T(alloc) + T(I/O) > > However, if we change our approach, we don't necessarily need to wait > for the DMA-BUF allocation to complete before initiating I/O. In fact, > during the allocation process, we already hold a portion of the page, > which means that waiting for subsequent page allocations to complete > before carrying out file reads is actually unfair to the pages that have > already been allocated. > > The allocation of pages is sequential, and the reading of the file is > also sequential, with the content and size corresponding to the file. > This means that the memory location for each page, which holds the > content of a specific position in the file, can be determined at the > time of allocation. > > However, to fully leverage I/O performance, it is best to wait and > gather a certain number of pages before initiating batch processing. > > The default gather size is 128MB. So, ever gathered can see as a file read > work, it maps the gather page to the vmalloc area to obtain a continuous > virtual address, which is used as a buffer to store the contents of the > corresponding file. So, if using direct I/O to read a file, the file > content will be written directly to the corresponding dma-buf buffer memory > without any additional copying.(compare to pipe buffer.) > > Consider other ways to read into dma-buf. If we assume reading after mmap > dma-buf, we need to map the pages of the dma-buf to the user virtual > address space. Also, udmabuf memfd need do this operations too. > Even if we support sendfile, the file copy also need buffer, you must > setup it. > So, mapping pages to the vmalloc area does not incur any additional > performance overhead compared to other methods.[6] > > Certainly, the administrator can also modify the gather size through patch5. > > The formula for the time taken for system_heap buffer allocation and > file reading through async_read is as follows: > > T(total) = T(first gather page) + Max(T(remain alloc), T(I/O)) > > Compared to the synchronous read: > T(total) = T(alloc) + T(I/O) > > If the allocation time or I/O time is long, the time difference will be > covered by the maximum value between the allocation and I/O. The other > party will be concealed. > > Therefore, the larger the size of the file that needs to be read, the > greater the corresponding benefits will be. > > How to use > === > Consider the current pathway for loading model files into DMA-BUF: > 1. open dma-heap, get heap fd > 2. open file, get file_fd(can't use O_DIRECT) > 3. use file len to allocate dma-buf, get dma-buf fd > 4. mmap dma-buf fd, get vaddr > 5. read(file_fd, vaddr, file_size) into dma-buf pages > 6. share, attach, whatever you want > > Use DMA_HEAP_ALLOC_AND_READ_FILE JUST a little change: > 1. open dma-heap, get heap fd > 2. open file, get file_fd(buffer/direct) > 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, set file_fd > instead of len. get dma-buf fd(contains file content) > 4. share, attach, whatever you want > > So, test it is easy. > > How to test > === > The performance comparison will be conducted for the following scenarios: > 1. normal > 2. udmabuf with [3] patch > 3. sendfile > 4. only patch 1 > 5. patch1 - patch4. > > normal: > 1. open dma-heap, get heap fd > 2. open file, get file_fd(can't use O_DIRECT) > 3. use file len to allocate dma-buf, get dma-buf fd > 4. mmap dma-buf fd, get vaddr > 5. read(file_fd, vaddr, file_size) into dma-buf pages > 6. share, attach, whatever you want > > UDMA-BUF step: > 1. memfd_create > 2. open file(buffer/direct) > 3. udmabuf create > 4. mmap memfd > 5. read file into memfd vaddr > > Sendfile step(need suit splice_write/write_iter, just use to compare): > 1. open dma-heap, get heap fd > 2. open file, get file_fd(buffer/direct) > 3. use file len to allocate dma-buf, get dma-buf fd > 4. sendfile file_fd to dma-buf fd > 6. share, attach, whatever you want > > patch1/patch1-4: > 1. open dma-heap, get heap fd > 2. open file, get file_fd(buffer/direct) > 3. allocate dma-buf with DMA_HEAP_ALLOC_AND_READ_FILE heap flag, set file_fd > instead of len. get dma-buf fd(contains file content) > 4. share, attach, whatever you want > > You can create a file to test it. Compare the performance gap between the two. > It is best to compare the differences in file size from KB to MB to GB. > > The following test data will compare the performance differences between 512KB, > 8MB, 1GB, and 3GB under various scenarios. > > Performance Test > === > 12G RAM phone > UFS4.0(the maximum speed is 4GB/s. ), > f2fs > kernel 6.1 with patch[7] (or else, can't support kvec direct I/O read.) > no memory pressure. > drop_cache is used for each test. > > The average of 5 test results: > | scheme-size | 512KB(ns) | 8MB(ns) | 1GB(ns) | 3GB(ns) | > | ------------------- | ---------- | ---------- | ------------- | ------------- | > | normal | 2,790,861 | 14,535,784 | 1,520,790,492 | 3,332,438,754 | > | udmabuf buffer I/O | 1,704,046 | 11,313,476 | 821,348,000 | 2,108,419,923 | > | sendfile buffer I/O | 3,261,261 | 12,112,292 | 1,565,939,938 | 3,062,052,984 | > | patch1-4 buffer I/O | 2,064,538 | 10,771,474 | 986,338,800 | 2,187,570,861 | > | sendfile direct I/O | 12,844,231 | 37,883,938 | 5,110,299,184 | 9,777,661,077 | > | patch1 direct I/O | 813,215 | 6,962,092 | 2,364,211,877 | 5,648,897,554 | > | udmabuf direct I/O | 1,289,554 | 8,968,138 | 921,480,784 | 2,158,305,738 | > | patch1-4 direct I/O | 1,957,661 | 6,581,999 | 520,003,538 | 1,400,006,107 | > > So, based on the test results: > > When the file is large, the patchset has the highest performance. > Compared to normal, patchset is a 50% improvement; > Compared to normal, patch1 only showed a degradation of 41%. > patch1 typical performance breakdown is as follows: > 1. alloc cost 188,802,693 ns > 2. vmap cost 42,491,385 ns > 3. file read cost 4,180,876,702 ns > Therefore, directly performing a single direct I/O read on a large file > may not be the most optimal way for performance. > > The performance of direct I/O implemented by the sendfile method is the worst. > > When file size is small, The difference in performance is not > significant. This is consistent with expectations. > > > > Suggested use cases > === > 1. When there is a need to read large files and system resources are scarce, > especially when the size of memory is limited.(GB level) In this > scenario, using direct I/O for file reading can even bring performance > improvements.(may need patch2-3) > 2. For embedded devices with limited RAM, using direct I/O can save system > resources and avoid unnecessary data copying. Therefore, even if the > performance is lower when read small file, it can still be used > effectively. > 3. If there is sufficient memory, pinning the page cache of the model files > in memory and placing file in the EROFS file system for read-only access > maybe better.(EROFS do not support direct I/O) > > > Changlog > === > v1 [8] > v1->v2: > Uses the heap flag method for alloc and read instead of adding a new > DMA-buf ioctl command. [9] > Split the patchset to facilitate review and test. > patch 1 implement alloc and read, offer heap flag into it. > patch 2-4 offer async read > patch 5 can change gather limit. > > Reference > === > [1] https://lore.kernel.org/all/0393cf47-3fa2-4e32-8b3d-d5d5bdece298@amd.com/ > [2] https://lore.kernel.org/all/ZpTnzkdolpEwFbtu@phenom.ffwll.local/ > [3] https://lore.kernel.org/all/20240725021349.580574-1-link@vivo.com/ > [4] https://lore.kernel.org/all/Zpf5R7fRZZmEwVuR@infradead.org/ > [5] https://lore.kernel.org/all/ZpiHKY2pGiBuEq4z@infradead.org/ > [6] https://lore.kernel.org/all/9b70db2e-e562-4771-be6b-1fa8df19e356@amd.com/ > [7] https://patchew.org/linux/20230209102954.528942-1-dhowells@redhat.com/20230… > [8] https://lore.kernel.org/all/20240711074221.459589-1-link@vivo.com/ > [9] https://lore.kernel.org/all/5ccbe705-883c-4651-9e66-6b452c414c74@amd.com/ > > Huan Yang (5): > dma-buf: heaps: Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag > dma-buf: heaps: Introduce async alloc read ops > dma-buf: heaps: support alloc async read file > dma-buf: heaps: system_heap alloc support async read > dma-buf: heaps: configurable async read gather limit > > drivers/dma-buf/dma-heap.c | 552 +++++++++++++++++++++++++++- > drivers/dma-buf/heaps/system_heap.c | 70 +++- > include/linux/dma-heap.h | 53 ++- > include/uapi/linux/dma-heap.h | 11 +- > 4 files changed, 673 insertions(+), 13 deletions(-) > > > base-commit: 931a3b3bccc96e7708c82b30b2b5fa82dfd04890

2 years, 3 months

Re: [PATCH v2] kselftests: dmabuf-heaps: Ensure the driver name is null-terminated

by Daniel Vetter

On Mon, Jul 29, 2024 at 10:46:04AM +0800, Zenghui Yu wrote: > Even if a vgem device is configured in, we will skip the import_vgem_fd() > test almost every time. > > TAP version 13 > 1..11 > # Testing heap: system > # ======================================= > # Testing allocation and importing: > ok 1 # SKIP Could not open vgem -1 > > The problem is that we use the DRM_IOCTL_VERSION ioctl to query the driver > version information but leave the name field a non-null-terminated string. > Terminate it properly to actually test against the vgem device. > > While at it, let's check the length of the driver name is exactly 4 bytes > and return early otherwise (in case there is a name like "vgemfoo" that > gets converted to "vgem\0" unexpectedly). > > Signed-off-by: Zenghui Yu <yuzenghui(a)huawei.com> > --- > * From v1 [1]: > - Check version.name_len is exactly 4 bytes and return early otherwise > > [1] https://lore.kernel.org/r/20240708134654.1725-1-yuzenghui@huawei.com Thanks for your patch, I'll push it to drm-misc-next-fixes. > P.S., Maybe worth including the kselftests file into "DMA-BUF HEAPS > FRAMEWORK" MAINTAINERS entry? Good idea, want to do the patch for that too? Cheers, Sima > > tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c > index 5f541522364f..5d0a809dc2df 100644 > --- a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c > +++ b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c > @@ -29,9 +29,11 @@ static int check_vgem(int fd) > version.name = name; > > ret = ioctl(fd, DRM_IOCTL_VERSION, &version); > - if (ret) > + if (ret || version.name_len != 4) > return 0; > > + name[4] = '\0'; > + > return !strcmp(name, "vgem"); > } > > -- > 2.33.0 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch

2 years, 3 months

Re: (subset) [PATCH v7 03/16] dt-bindings: mfd: mediatek: Add codec property for MT6357 PMIC

by Lee Jones

On Mon, 22 Jul 2024 08:53:32 +0200, Alexandre Mergnat wrote: > Add the audio codec sub-device. This sub-device is used to set the > optional voltage values according to the hardware. > The properties are: > - Setup of microphone bias voltage. > - Setup of the speaker pin pull-down. > > Also, add the audio power supply property which is dedicated for > the audio codec sub-device. > > [...] Applied, thanks! [03/16] dt-bindings: mfd: mediatek: Add codec property for MT6357 PMIC commit: 3821149eb101fe2d45a4697659e60930828400d8 -- Lee Jones [李琼斯]

2 years, 3 months

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