2023-06-14 01:05:46

by Ed Tsai (蔡宗軒)

Subject: [PATCH v3] blk-mq: check on cpu id when there is only one ctx mapping

commit f168420c62e7 ("blk-mq: don't redirect completion for hctx withs
only one ctx mapping") When nvme applies a 1:1 mapping of hctx and ctx,
there will be no remote request.

But for ufs, the submission and completion queues could be asymmetric.
(e.g. Multiple SQs share one CQ) Therefore, 1:1 mapping of hctx and
ctx won't complete request on the submission cpu. In this situation,
this nr_ctx check could violate the QUEUE_FLAG_SAME_FORCE, as a result,
check on cpu id when there is only one ctx mapping.

Signed-off-by: Ed Tsai <[email protected]>
Signed-off-by: Po-Wen Kao <[email protected]>
Suggested-by: Keith Busch <[email protected]>

---
block/blk-mq.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 41f7e2b500bd..ecc30ebe9483 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1176,7 +1176,8 @@ bool blk_mq_complete_request_remote(struct request *rq)
* or a polled request, always complete locally,
* it's pointless to redirect the completion.
*/
- if (rq->mq_hctx->nr_ctx == 1 ||
+ if ((rq->mq_hctx->nr_ctx == 1 &&
+ rq->mq_ctx->cpu == raw_smp_processor_id()) ||
rq->cmd_flags & REQ_POLLED)
return false;

--
2.18.0

2023-06-14 06:32:17

by Christoph Hellwig

Subject: Re: [PATCH v3] blk-mq: check on cpu id when there is only one ctx mapping

This looks fine to me:

Reviewed-by: Christoph Hellwig <[email protected]>
> - if (rq->mq_hctx->nr_ctx == 1 ||
> + if ((rq->mq_hctx->nr_ctx == 1 &&
> + rq->mq_ctx->cpu == raw_smp_processor_id()) ||
> rq->cmd_flags & REQ_POLLED)

But please fix the incorrct indentation in the existing code here
please while you're at it (maybe Jens can just fold it in):

if ((rq->mq_hctx->nr_ctx == 1 &&
rq->mq_ctx->cpu == raw_smp_processor_id()) ||
(rq->cmd_flags & REQ_POLLED))

2023-06-14 17:59:21

by Jens Axboe

Subject: Re: [PATCH v3] blk-mq: check on cpu id when there is only one ctx mapping

On Wed, 14 Jun 2023 08:25:29 +0800, Ed Tsai wrote:
> commit f168420c62e7 ("blk-mq: don't redirect completion for hctx withs
> only one ctx mapping") When nvme applies a 1:1 mapping of hctx and ctx,
> there will be no remote request.
>
> But for ufs, the submission and completion queues could be asymmetric.
> (e.g. Multiple SQs share one CQ) Therefore, 1:1 mapping of hctx and
> ctx won't complete request on the submission cpu. In this situation,
> this nr_ctx check could violate the QUEUE_FLAG_SAME_FORCE, as a result,
> check on cpu id when there is only one ctx mapping.
>
> [...]

Applied, thanks!

[1/1] blk-mq: check on cpu id when there is only one ctx mapping
commit: 30654614f3d27230200b1650f6025a2ce67900b4

Best regards,
--
Jens Axboe