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| author | Yu Kuai <yukuai3@huawei.com> | 2022-05-13 10:35:07 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2022-05-16 11:39:20 -0600 |
| commit | ddc25c86b466d2359b57bc7798f167baa1735a44 (patch) | |
| tree | 42e97d04b7d1155d8c68e00b876780930ed7bc61 /block | |
| parent | 181490d5321806e537dc5386db5ea640b826bf78 (diff) | |
| download | linux-stable-ddc25c86b466d2359b57bc7798f167baa1735a44.tar.gz linux-stable-ddc25c86b466d2359b57bc7798f167baa1735a44.tar.bz2 linux-stable-ddc25c86b466d2359b57bc7798f167baa1735a44.zip | |
block, bfq: make bfq_has_work() more accurate
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>
Diffstat (limited to 'block')
| -rw-r--r-- | block/bfq-iosched.c | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 62180dda6bf9..92f0a829a804 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -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) |