Commit b6d2b054 authored by Bart Van Assche's avatar Bart Van Assche Committed by Jens Axboe
Browse files

mq-deadline: Fix request accounting 



The block layer may call the I/O scheduler .finish_request() callback
without having called the .insert_requests() callback. Make sure that the
mq-deadline I/O statistics are correct if the block layer inserts an I/O
request that bypasses the I/O scheduler. This patch prevents that lower
priority I/O is delayed longer than necessary for mixed I/O priority
workloads.

Cc: Niklas Cassel <Niklas.Cassel@wdc.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Reported-by: default avatarNiklas Cassel <Niklas.Cassel@wdc.com>
Fixes: 08a9ad8b ("block/mq-deadline: Add cgroup support")
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210824170520.1659173-1-bvanassche@acm.org


Reviewed-by: default avatarNiklas Cassel <niklas.cassel@wdc.com>
Tested-by: default avatarNiklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a9ed27a7

block/mq-deadline.c

+11 −5
Original line number Diff line number Diff line
@@ -711,6 +711,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, 


	prio = ioprio_class_to_prio[ioprio_class];

	dd_count(dd, inserted, prio);

	rq->elv.priv[0] = (void *)(uintptr_t)1;



	if (blk_mq_sched_try_insert_merge(q, rq, &free)) {

		blk_mq_free_requests(&free);
@@ -759,12 +760,10 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx, 
	spin_unlock(&dd->lock);

}



/*

 * Nothing to do here. This is defined only to ensure that .finish_request

 * method is called upon request completion.

 */

/* Callback from inside blk_mq_rq_ctx_init(). */

static void dd_prepare_request(struct request *rq)

{

	rq->elv.priv[0] = NULL;

}



/*
@@ -791,6 +790,13 @@ static void dd_finish_request(struct request *rq) 
	const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];

	struct dd_per_prio *per_prio = &dd->per_prio[prio];



	/*

	 * The block layer core may call dd_finish_request() without having

	 * called dd_insert_requests(). Hence only update statistics for

	 * requests for which dd_insert_requests() has been called. See also

	 * blk_mq_request_bypass_insert().

	 */

	if (rq->elv.priv[0])

		dd_count(dd, completed, prio);



	if (blk_queue_is_zoned(q)) {