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block, bfq: make bfq_has_work() more accurate

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bfq_has_work() is using busy_queues currently, which is not accurate
because bfq_queue is busy doesn't represent that it has requests. Since
bfqd aready has a counter 'queued' to record how many requests are in
bfq, use it instead of busy_queues.

Noted that bfq_has_work() can be called with 'bfqd->lock' held, thus the
lock can't be held in bfq_has_work() to protect 'bfqd->queued'.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220513023507.2625717-3-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2022-05-13 10:35:07 +08:00 committed by Jens Axboe
parent 181490d532
commit ddc25c86b4
1 changed files with 12 additions and 4 deletions
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16
block/bfq-iosched.c
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@ -2204,7 +2204,11 @@ static void bfq_add_request(struct request *rq)
bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
bfqq->queued[rq_is_sync(rq)]++;
bfqd->queued++;
/*
* Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
* may be read without holding the lock in bfq_has_work().
*/
WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) {
bfq_check_waker(bfqd, bfqq, now_ns);
@ -2396,7 +2400,11 @@ static void bfq_remove_request(struct request_queue *q,
if (rq->queuelist.prev != &rq->queuelist)
list_del_init(&rq->queuelist);
bfqq->queued[sync]--;
bfqd->queued--;
/*
* Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
* may be read without holding the lock in bfq_has_work().
*/
WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
elv_rb_del(&bfqq->sort_list, rq);
elv_rqhash_del(q, rq);
@ -5057,11 +5065,11 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
/*
* Avoiding lock: a race on bfqd->busy_queues should cause at
* Avoiding lock: a race on bfqd->queued should cause at
* most a call to dispatch for nothing
*/
return !list_empty_careful(&bfqd->dispatch) ||
bfq_tot_busy_queues(bfqd) > 0;
READ_ONCE(bfqd->queued);
}
static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)