2023-05-31 08:48:03

by Ed Tsai (蔡宗軒)

Subject: [PATCH v2] blk-mq: check on cpu id when there is only one ctx mapping

commit f168420 ("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]>
Change-Id: I4f95d7538532f72dcb20dacfdd639c97951c2729
---
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

2023-05-31 10:23:04

by Alexandre Mergnat

Subject: Re: [PATCH v2] blk-mq: check on cpu id when there is only one ctx mapping

On 31/05/2023 10:38, Ed Tsai wrote:
> commit f168420 ("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.

Reviewed-by: Alexandre Mergnat <[email protected]>

--
Regards,
Alexandre