On 14/05/2021 03:20, Ming Lei wrote:
In case of shared sbitmap, request won't be held in plug list any more
sine commit 32bc15afed04 ("blk-mq: Facilitate a shared sbitmap per
tagset"), this way makes request merge from flush plug list & batching
submission not possible, so cause performance regression.
Yanhui reports performance regression when running sequential IO
test(libaio, 16 jobs, 8 depth for each job) in VM, and the VM disk
is emulated with image stored on xfs/megaraid_sas.
Fix the issue by recovering original behavior to allow to hold request
in plug list.
Hi Ming,
Since testing v5.13-rc2, I noticed that this patch made the hang I was
seeing disappear:
https://lore.kernel.org/linux-scsi/3d72d64d-314f-9d34-e039-7e508b2abe1b@xxxxxxxxxx/
I don't think that problem is solved, though.
So I wonder about throughput performance (I had hoped to test before it
was merged). I only have 6x SAS SSDs at hand, but I see some significant
changes (good and bad) for mq-deadline for hisi_sas:
Before 620K (read), 300K IOPs (randread)
After 430K (read), 460-490K IOPs (randread)
none IO sched is always about 450K (read) and 500K (randread)
Do you guys have any figures? Are my results as expected?
Thanks,
John
Cc: Yanhui Ma <yama@xxxxxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: kashyap.desai@xxxxxxxxxxxx
Fixes: 32bc15afed04 ("blk-mq: Facilitate a shared sbitmap per tagset")
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ae7f5ee41cd3..baf7a9546068 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2236,8 +2236,9 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
/* Bypass scheduler for flush requests */
blk_insert_flush(rq);
blk_mq_run_hw_queue(data.hctx, true);
- } else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs ||
- !blk_queue_nonrot(q))) {
+ } else if (plug && (q->nr_hw_queues == 1 ||
+ blk_mq_is_sbitmap_shared(rq->mq_hctx->flags) ||
+ q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {
/*
* Use plugging if we have a ->commit_rqs() hook as well, as
* we know the driver uses bd->last in a smart fashion.
