Linaro-mm-sig April 2011

linaro-mm-sig@lists.linaro.org

38 participants
8 discussions

by Sree Kumar

Thanks Jesse for initiating the mailing list. We need to address the requirements of Graphics and Multimedia Accelerators (IPs). What we really need is a permanent solution (at upstream) which accommodates the following requirements and conforms to Graphics and Multimedia use cases. 1.Mechanism to map/unmap the memory. Some of the IPs’ have the ability to address virtual memory and some can address only physically contiguous address space. We need to address both these cases. 2.Mechanism to allocate and release memory. 3.Method to share the memory (ZERO copy is a MUST for better performance) between different device drivers (example output of camera to multimedia encoder). 4.Method to share the memory with different processes in userspace. The sharing mechanism should include built-in security features. Are there any special requirements from V4L or DRM perspectives? Thanks, Sree

13 years, 10 months

Requirements for Memory Management

by 이상현

Hi all, The followings are Samsung S.LSI's requirement for unified memory manager. 1. User space API 1.1. New memory management(MM) features should includes followings to the user space.: UMP A. user space API for memory allocation from system memory: UMP Any user process can allocate memory from kernel space by new MM model. B. user space API for cache operations: flush, clean, invalidate Any user process can do cache operation on the allocated memory. C. user space API for mapping memory attribute as cacheable When the system memory mapped into the user space, user process can set its property as cacheable. D. user space API for mapping memory attribute as non-cacheable When the system memory mapped into the user space, user process can set its property as non-cacheable. 1.2. Inter-process memory sharing: UMP New MM features should provide memory sharing between user process. A. Memory allocated by user space can be shared between user processes. B. Memory allocated by kernel space can be shared between user processes. 2. Kernel space API New MM features should includes followings to the kernel space.: CMA, VCMM 2-1. Physically memory allocator A. kernel space API for contiguous memory allocation: CMA(*) B. kernel space API for non-contiguous memory allocation: VCMM (*) C. start address alignment: CMA, VCMM D. selectable allocating region: CMA *refer to the bottom's extension. 2-2. Device virtual address management: VCMM New MM features should provide the way of managing device virtual memory address as like followings: A. IOMMU(System MMU) support IOMMU is a kind of memory MMU, but IOMMU is dedicated for each device. B. device virtual address mapping for each device C. virtual memory allocation D. mapping / remapping between phys and device virtual address E. dedicated device virtual address space for each device F. address translation between address space U.V / \ K.V - P.A \ / D.V U.V: User space address K.A: Kernel space address P.A: Physical address D.V: Device virtual address 3. Extensions A. extension for custom physical memory allocator B. extension for custom MMU controller ------------------------------------------------------------------------- You can find the implementation in the following git repository. http://git.kernel.org/?p=linux/kernel/git/kki_ap/linux-2.6- samsung.git;a=tree;hb=refs/heads/2.6.36-samsung 1. UMP (Unified Memory Provider) - The UMP is an auxiliary component which enables memory to be shared across different applications, drivers and hardware components. - http://blogs.arm.com/multimedia/249-making-the-mali-gpu-device-driver- open-source/page__cid__133__show__newcomment/ - Suggested by ARM, Not submitted yet. - implementation drivers/media/video/samsung/ump/* 2. VCMM (Virtual Contiguous Memory Manager) - The VCMM is a framework to deal with multiple IOMMUs in a system with intuitive and abstract objects - Submitted by Michal Nazarewicz @Samsung-SPRC - Also submitted by KyongHo Cho @Samsung-SYS.LSI - http://article.gmane.org/gmane.linux.kernel.mm/56912/match=vcm - implementation include/linux/vcm.h include/linux/vcm-drv.h mm/vcm.c arch/arm/plat-s5p/s5p-vcm.c arch/amr/plat-s5p/include/plat/s5p-vcm.h 3. CMA (Contiguous Memory Allocator) - The Contiguous Memory Allocator (CMA) is a framework, which allows setting up a machine-specific configuration for physically-contiguous memory management. Memory for devices is then allocated according to that configuration. - http://lwn.net/Articles/396702/ - http://www.spinics.net/lists/linux-media/msg26486.html - Submitted by Michal Nazarewicz @Samsung-SPRC - implementation mm/cma.c include/linux/cma.h 4. SYS.MMU - System MMU supports address transition from VA to PA. - http://thread.gmane.org/gmane.linux.kernel.samsung-soc/3909 - Submitted by Sangbeom Kim - Merged by Kukjin Kim, ARM/S5P ARM ARCHITECTURES maintainer - implementation arch/arm/plat-s5p/sysmmu.c arch/arm/plat-s5p/include/plat/sysmmu.h

13 years, 11 months

[RFC] ARM DMA mapping TODO, v1

by Arnd Bergmann

I think the recent discussions on linaro-mm-sig and the BoF last week at ELC have been quite productive, and at least my understanding of the missing pieces has improved quite a bit. This is a list of things that I think need to be done in the kernel. Please complain if any of these still seem controversial: 1. Fix the arm version of dma_alloc_coherent. It's in use today and is broken on modern CPUs because it results in both cached and uncached mappings. Rebecca suggested different approaches how to get there. 2. Implement dma_alloc_noncoherent on ARM. Marek pointed out that this is needed, and it currently is not implemented, with an outdated comment explaining why it used to not be possible to do it. 3. Convert ARM to use asm-generic/dma-mapping-common.h. We need both IOMMU and direct mapped DMA on some machines. 4. Implement an architecture independent version of dma_map_ops based on the iommu.h API. As Joerg mentioned, this has been missing for some time, and it would be better to do it once than for each IOMMU separately. This is probably a lot of work. 5. Find a way to define per-device IOMMUs, if that is not actually possible already. We had conflicting statements for this. 6. Implement iommu_ops for each of the ARM platforms that has an IOMMU. Needs some modifications for MSM and a rewrite for OMAP. Implementation for Samsung is under work. 7. Extend the dma_map_ops to have a way for mapping a buffer from dma_alloc_{non,}coherent into user space. We have not discussed that yet, but after thinking this for some time, I believe this would be the right approach to map buffers into user space from code that doesn't care about the underlying hardware. After all these are in place, building anything on top of dma_alloc_{non,}coherent should be much easier. The question of passing buffers between V4L and DRM is still completely unsolved as far as I can tell, but that discussion might become more focused if we can agree on the above points and assume that it will be done. I expect that I will have to update the list above as people point out mistakes in my assumptions. Arnd

13 years, 11 months

Memory region attribute bits and multiple mappings

by Rebecca Schultz Zavin

Hey all, While we are working out requirements, I was hoping to get some more information about another related issue that keeps coming up on mailing lists and in discussions. ARM has stated that if you have the same physical memory mapped with two different sets of attribute bits you get undefined behavior. I think it's going to be a requirement that some of the memory allocated via the unified memory manager is mapped uncached. However, because all of memory is mapped cached into the unity map at boot, we already have two mappings with different attributes. I want to understand the mechanism of the problem, because none of the solutions I can come up with are particularly nice. I'd also like to know exactly which architectures are affected, since the fix may be costly in performance, memory or both. Can someone at ARM explain to me why this causes a problem. I have a theory, but it's mostly a guess. I especially want to understand if it's still a problem if we never access the memory via the mapping in the unity map. I know speculative prefetching is part of the issue, so I assume older architectures without that feature don't exhibit this behaviour If we really need all mappings of physical memory to have the same cache attribute bits, I see three workarounds: 1- set aside memory at boot that never gets mapped by the kernel. The unified memory manager can then ensure there's only one mapping at a time. Obvious drawbacks here are that you have to statically partition your system into memory you want accessible to the unified memory manager and memory you don't. This may not be that big a deal, since most current solutions, pmem, cmem, et al basically do this. I can say that on Android devices running on a high resolution display (720p and above) we're easily talking about needing 256M of memory or more to dedicate to this. 2- use highmem pages only for the unified memory manager. Highmem pages only get mapped on demand. This has some performance costs when the kernel allocates other metadata in highmem. Most embedded systems still don't have enough memory to need highmem, though I'm guessing that'll follow the current trend and shift in the next couple of years. 3- fix up the unity mapping so the attribute bits match those desired by the unified memory manger. This could be done by removing pages from the unity map. It's complicated by the fact that the unity map makes use of large pages, sections and supersections to reduce tlb pressure. I don't think this is impossible if we restrict the set of contexts from which it can happen, but I'm imagining that we will also need to maintain some kind of pool of memory we've moved from cached to uncached since the process is likely to be expensive. Quite likely we will have to iterate over processes and update all their top level page tables. These all have drawbacks, so I'd like to really understand the problem before pursuing them. Can the linaro folks find someone who can explain the problem in more detail? Thanks, Rebecca

13 years, 11 months

Budapest summit scheduling

by Jesse Barker

Hi all, For those that are interested in or required to attend additional sessions at the larger LDS or UDS events, at the request of the folks managing the scheduling, I've created blueprints, one for each day, to track the sessions. The reason for this is that the autoscheduler will attempt to honor people's "essential" participation, so if you are marked "essential" for both the mini-summit and another track session, there is increased likelihood that you will not have a conflict. I have limited editorial say in the scheduling, so if there are critical conflicts, I can try to help resolve them. I've put the links to the blueprints under "registration" in the mini-summit event on https://wiki.linaro.org/Events, but for convenience, here they are: https://blueprints.edge.launchpad.net/linaro-graphics-wg/+spec/linaro-graph… https://blueprints.edge.launchpad.net/linaro-graphics-wg/+spec/linaro-graph… https://blueprints.edge.launchpad.net/linaro-graphics-wg/+spec/linaro-graph… I'm still tracking the agenda on the Linaro wiki, but will be moving the day's agenda to each blueprint as the event approaches. cheers, Jesse

13 years, 11 months

CFP: Budapest Mini-summit update

by Jesse Barker

Hi all, The good news is that largely everything is as I announced previously. The tracks have been cleaned up a bit, so the memory management mini-summit is now driven out of the Linaro Graphics track, but the room (Ond) and schedule (M-W afternoons) is still the same. All the info you need on the schedule is here: http://summit.ubuntu.com/uds-o/ The room is supposed to have a projector, be mic'd for live audio and have an IRC channel. Those participating remotely will be interested in the details around the audio and IRC access here: http://uds.ubuntu.com/participate/remote/ A link for the mini-summit event found here: https://wiki.linaro.org/Events goes to the (work in progress) agenda and there is a registration link as well. Please let me know if I've missed any components that need representation, if there are some on there that you feel don't need it, or if there are additional items you'd like to see on the agenda. I have 2 requests of the people that will participate in person: 1) Please "register" to indicate you'll be there in person (or even if you plan on participating remotely). There are a few reasons for this, but the critical one is to make sure we have a big enough room. 2) Sign-up to represent a component, at least in the overview sessions. This is important for sane discussion afterwards. If you don't or can't get write access to the Linaro wiki, just send me email directly and I'll do it by proxy. Also, if you have material that you will "show" people (slides, etc.), please send it to the list ahead of time for the benefit of those participating remotely. Finally, the "project page" for this effort is here on the Linaro wiki: https://wiki.linaro.org/OfficeofCTO/MemoryManagement Thanks again to everyone for their contributions. cheers, Jesse

13 years, 11 months

Split GEM from the rest of DRM

by Jordan Crouse

During the MM BoF at ELC, it seemed to me that one of the things that scared most ARM vendors away from GEM in the first place is that was perceived to be too closely married to the rest of DRM (especially KMS). I know that some might argue that isn't necessarily true and we can go back and forth on that point, but I think it is still valuable to ask this question: How feasible is it to break out the GEM portion of DRM (essentially drm_gem.c) and put it into its own subsystem or library component for use by a DRM or a non DRM component. What parts would a non DRM component be missing to use GEM effectively (authentication comes to mind)? Jordan

13 years, 11 months

Mini-summit (incomplete) details

by Jesse Barker

Hi all, I'll be rolling out the details around the Budapest mini-summit as I get them, so there will be more to follow. You can check out the overall schedule here: http://summit.ubuntu.com/uds-o/ As of right now, viewing by track, the mini-summit is listed in the "other" track, though, this may change over the next few days. Viewing the schedule by day, we are right after lunch through the end of the day on Monday-Wednesday (there are plenaries scheduled for immediately after lunch, but unless there are strong objections, I'd argue for going straight into the summit). And finally, by room, we are in "Ond". For those that will be participating remotely, I don't yet have the details on how to tune in to the audio channel, but the IRC channel will be named for the room we're in; I expect to have the rest of those details later this week or early next. I'll also be creating a blueprint on Launchpad to hold our outline, agenda, notes, minutes, etc. (last cycle we used "gobby" to take notes live, but there were stability issues with the server, so we'll see how that goes). Based upon the discussion from ELC, I would expect much of the first day to be component/subsystem overview; I really think that will be critical to finalizing sane requirements. These discussions do not have to wait until Budapest. If there are questions you would like to see answered, send them along. Also, if folks that are attending in person could let me know directly, it would be good to get an updated headcount of who is coming to make sure I don't need to argue for a bigger room. cheers, Jesse

13 years, 11 months

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Linaro-mm-sig April 2011