On Fri 13-05-22 10:35:07, Yu Kuai wrote:
> 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@xxxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> block/bfq-iosched.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 61750696e87f..740dd83853a6 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -2210,7 +2210,11 @@ 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);
> @@ -2402,7 +2406,11 @@ 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);
> @@ -5063,11 +5071,11 @@ 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)
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
