From: Jan Kara <jack@suse.cz>
To: Yu Kuai <yukuai3@huawei.com>
Cc: jack@suse.cz, paolo.valente@linaro.org, axboe@kernel.dk,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
yi.zhang@huawei.com
Subject: Re: [PATCH -next 2/2] block, bfq: make bfq_has_work() more accurate
Date: Wed, 11 May 2022 16:08:32 +0200 [thread overview]
Message-ID: <20220511140832.w6eqphw5uepre5ws@quack3.lan> (raw)
In-Reply-To: <20220510131629.1964415-3-yukuai3@huawei.com>
On Tue 10-05-22 21:16:29, 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@huawei.com>
So did you find this causing any real problem? Because bfq queue is
accounted among busy queues once bfq_add_bfqq_busy() is called. And that
happens once a new request is inserted into the queue so it should be very
similar to bfqd->queued.
Honza
> ---
> block/bfq-iosched.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 61750696e87f..1d2f8110c26b 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5063,11 +5063,11 @@ 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@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2022-05-11 14:08 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 13:16 [PATCH -next 0/2] block, bfq: make bfq_has_work() more accurate Yu Kuai
2022-05-10 13:16 ` [PATCH -next 1/2] block, bfq: protect 'bfqd->queued' by 'bfqd->lock' Yu Kuai
2022-05-11 13:52 ` Jan Kara
2022-05-10 13:16 ` [PATCH -next 2/2] block, bfq: make bfq_has_work() more accurate Yu Kuai
2022-05-11 14:08 ` Jan Kara [this message]
2022-05-12 1:30 ` yukuai (C)
2022-05-12 17:10 ` Jan Kara
2022-05-13 1:08 ` yukuai (C)
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