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authorJan Kara <jack@suse.cz>2021-01-11 17:47:17 +0100
committerJens Axboe <axboe@kernel.dk>2021-01-24 18:19:46 -0700
commitb6e68ee82585f2ee890b0a897a6aacbf49a467bb (patch)
tree4eef276f577fcadb7c02563a771655651c605b49 /block/kyber-iosched.c
parent5ac83c644f5fb924f0b2c09102ab82fc788f8411 (diff)
blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues
Currently when non-mq aware IO scheduler (BFQ, mq-deadline) is used for a queue with multiple HW queues, the performance it rather bad. The problem is that these IO schedulers use queue-wide locking and their dispatch function does not respect the hctx it is passed in and returns any request it finds appropriate. Thus locality of request access is broken and dispatch from multiple CPUs just contends on IO scheduler locks. For these IO schedulers there's little point in dispatching from multiple CPUs. Instead dispatch always only from a single CPU to limit contention. Below is a comparison of dbench runs on XFS filesystem where the storage is a raid card with 64 HW queues and to it attached a single rotating disk. BFQ is used as IO scheduler: clients MQ SQ MQ-Patched Amean 1 39.12 (0.00%) 43.29 * -10.67%* 36.09 * 7.74%* Amean 2 128.58 (0.00%) 101.30 * 21.22%* 96.14 * 25.23%* Amean 4 577.42 (0.00%) 494.47 * 14.37%* 508.49 * 11.94%* Amean 8 610.95 (0.00%) 363.86 * 40.44%* 362.12 * 40.73%* Amean 16 391.78 (0.00%) 261.49 * 33.25%* 282.94 * 27.78%* Amean 32 324.64 (0.00%) 267.71 * 17.54%* 233.00 * 28.23%* Amean 64 295.04 (0.00%) 253.02 * 14.24%* 242.37 * 17.85%* Amean 512 10281.61 (0.00%) 10211.16 * 0.69%* 10447.53 * -1.61%* Numbers are times so lower is better. MQ is stock 5.10-rc6 kernel. SQ is the same kernel with megaraid_sas.host_tagset_enable=0 so that the card advertises just a single HW queue. MQ-Patched is a kernel with this patch applied. You can see multiple hardware queues heavily hurt performance in combination with BFQ. The patch restores the performance. Signed-off-by: Jan Kara <jack@suse.cz> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/kyber-iosched.c')
-rw-r--r--block/kyber-iosched.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index dc89199bc8c6..c25c41d0d061 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -1029,6 +1029,7 @@ static struct elevator_type kyber_sched = {
#endif
.elevator_attrs = kyber_sched_attrs,
.elevator_name = "kyber",
+ .elevator_features = ELEVATOR_F_MQ_AWARE,
.elevator_owner = THIS_MODULE,
};