On Thu, Mar 10, 2022 at 2:10 PM Song Liu song@kernel.org wrote:
On Wed, Mar 9, 2022 at 11:23 PM Song Liu song@kernel.org wrote:
On Wed, Mar 9, 2022 at 10:48 PM Christoph Hellwig hch@infradead.org wrote:
On Tue, Mar 08, 2022 at 10:42:09PM -0800, Song Liu wrote:
RAID arrays check/repair operations benefit a lot from merging requests. If we only check the previous entry for merge attempt, many merge will be missed. As a result, significant regression is observed for RAID check and repair.
Fix this by checking more than just the previous entry when plug->multiple_queues == true.
But this also means really significant CPU overhead for all other workloads.
Would the following check help with these workloads?
if (!plug->multiple_queues) break;
This improves the check/repair speed of a 20-HDD raid6 from 19 MB/s to 103 MB/s.
What driver uses multiple queues for HDDs?
Can you explain the workload submitted by a md a bit better? I wonder if we can easily do the right thing straight in the md driver.
It is the md sync_thread doing check and repair. Basically, the md thread reads all the disks and computes parity from data.
Maybe we should add a new flag to struct blk_plug for this special case?
I meant something like:
diff --git c/block/blk-core.c w/block/blk-core.c index 1039515c99d6..4fb09243e908 100644 --- c/block/blk-core.c +++ w/block/blk-core.c @@ -1303,6 +1303,12 @@ void blk_finish_plug(struct blk_plug *plug) } EXPORT_SYMBOL(blk_finish_plug);
+void blk_plug_merge_aggressively(struct blk_plug *plug) +{
- plug->aggresive_merge = true;
+} +EXPORT_SYMBOL(blk_plug_merge_aggressively);
void blk_io_schedule(void) { /* Prevent hang_check timer from firing at us during very long I/O */
Missed one change:
--- c/block/blk-core.c +++ w/block/blk-core.c @@ -1188,6 +1188,7 @@ void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios) plug->multiple_queues = false; plug->has_elevator = false; plug->nowait = false; + plug->aggresive_merge = false; INIT_LIST_HEAD(&plug->cb_list);
/*