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blk-mq: don't handle non-flush requests in blk_insert_flush

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Return to the normal blk_mq_submit_bio flow if the bio did not end up
actually being a flush because the device didn't support it.  Note that
this is basically impossible to hit without special instrumentation given
that submit_bio_checks already clears these flags usually, so we'd need a
tight race to actually hit this code path.

With this the call to blk_mq_run_hw_queue for the flush requests can be
removed given that the actual flush requests are always issued via the
requeue workqueue which runs the queue unconditionally.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211019122553.2467817-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2021-10-19 14:25:53 +02:00 committed by Jens Axboe
parent dc5fc361d8
commit d92ca9d834
3 changed files with 13 additions and 15 deletions
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12
block/blk-flush.c
View File

@ -379,7 +379,7 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
* @rq is being submitted. Analyze what needs to be done and put it on the
* right queue.
*/
void blk_insert_flush(struct request *rq)
bool blk_insert_flush(struct request *rq)
{
struct request_queue *q = rq->q;
unsigned long fflags = q->queue_flags; /* may change, cache */
@ -409,7 +409,7 @@ void blk_insert_flush(struct request *rq)
*/
if (!policy) {
blk_mq_end_request(rq, 0);
return;
return true;
}
BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
@ -420,10 +420,8 @@ void blk_insert_flush(struct request *rq)
* for normal execution.
*/
if ((policy & REQ_FSEQ_DATA) &&
!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
blk_mq_request_bypass_insert(rq, false, false);
return;
}
!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH)))
return false;
/*
* @rq should go through flush machinery. Mark it part of flush
@ -439,6 +437,8 @@ void blk_insert_flush(struct request *rq)
spin_lock_irq(&fq->mq_flush_lock);
blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
spin_unlock_irq(&fq->mq_flush_lock);
return true;
}
/**

14
block/blk-mq.c
View File

@ -2532,14 +2532,12 @@ void blk_mq_submit_bio(struct bio *bio)
return;
}
if (unlikely(is_flush_fua)) {
struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
/* Bypass scheduler for flush requests */
blk_insert_flush(rq);
blk_mq_run_hw_queue(hctx, true);
} else if (plug && (q->nr_hw_queues == 1 ||
blk_mq_is_shared_tags(rq->mq_hctx->flags) ||
q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {
if (is_flush_fua && blk_insert_flush(rq))
return;
if (plug && (q->nr_hw_queues == 1 ||
blk_mq_is_shared_tags(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.

2
block/blk.h
View File

@ -236,7 +236,7 @@ void __blk_account_io_done(struct request *req, u64 now);
*/
#define ELV_ON_HASH(rq) ((rq)->rq_flags & RQF_HASHED)
void blk_insert_flush(struct request *rq);
bool blk_insert_flush(struct request *rq);
int elevator_switch_mq(struct request_queue *q,
struct elevator_type *new_e);