From: Bart Van Assche <bvanassche@acm.org>
To: Salman Qazi <sqazi@google.com>, Jens Axboe <axboe@kernel.dk>,
Ming Lei <ming.lei@redhat.com>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Jesse Barnes <jsbarnes@google.com>,
Gwendal Grignou <gwendal@google.com>,
Hannes Reinecke <hare@suse.com>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] block: Limit number of items taken from the I/O scheduler in one go
Date: Fri, 7 Feb 2020 07:26:49 -0800 [thread overview]
Message-ID: <5707b17f-e5d7-c274-de6a-694098c4e9a2@acm.org> (raw)
In-Reply-To: <20200206211222.83170-1-sqazi@google.com>
On 2020-02-06 13:12, Salman Qazi wrote:
> + *
> + * Returns true if hctx->dispatch was found non-empty and
> + * run_work has to be run again.
Please elaborate this comment and explain why this is necessary (to
avoid that flush processing is postponed forever).
> + * Returns true if hctx->dispatch was found non-empty and
> + * run_work has to be run again.
Same comment here.
> +again:
> + run_again = false;
> +
> /*
> * If we have previous entries on our dispatch list, grab them first for
> * more fair dispatch.
> @@ -208,19 +234,28 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
> blk_mq_sched_mark_restart_hctx(hctx);
> if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
> if (has_sched_dispatch)
> - blk_mq_do_dispatch_sched(hctx);
> + run_again = blk_mq_do_dispatch_sched(hctx);
> else
> - blk_mq_do_dispatch_ctx(hctx);
> + run_again = blk_mq_do_dispatch_ctx(hctx);
> }
> } else if (has_sched_dispatch) {
> - blk_mq_do_dispatch_sched(hctx);
> + run_again = blk_mq_do_dispatch_sched(hctx);
> } else if (hctx->dispatch_busy) {
> /* dequeue request one by one from sw queue if queue is busy */
> - blk_mq_do_dispatch_ctx(hctx);
> + run_again = blk_mq_do_dispatch_ctx(hctx);
> } else {
> blk_mq_flush_busy_ctxs(hctx, &rq_list);
> blk_mq_dispatch_rq_list(q, &rq_list, false);
> }
> +
> + if (run_again) {
> + if (!restarted) {
> + restarted = true;
> + goto again;
> + }
> +
> + blk_mq_run_hw_queue(hctx, true);
> + }
So this patch changes blk_mq_sched_dispatch_requests() such that it
iterates at most two times? How about implementing that loop with an
explicit for-loop? I think that will make
blk_mq_sched_dispatch_requests() easier to read. As you may know forward
goto's are accepted in kernel code but backward goto's are frowned upon.
Thanks,
Bart.
next prev parent reply other threads:[~2020-02-07 15:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 19:34 Hung tasks with multiple partitions Salman Qazi
2020-01-30 20:49 ` Bart Van Assche
2020-01-30 21:02 ` Salman Qazi
[not found] ` <20200203204554.119849-1-sqazi@google.com>
2020-02-03 20:59 ` [PATCH] block: Limit number of items taken from the I/O scheduler in one go Salman Qazi
2020-02-04 3:47 ` Bart Van Assche
2020-02-04 9:20 ` Ming Lei
2020-02-04 18:26 ` Salman Qazi
2020-02-04 19:37 ` Salman Qazi
2020-02-05 4:55 ` Ming Lei
2020-02-05 19:57 ` Salman Qazi
2020-02-06 10:18 ` Ming Lei
2020-02-06 21:12 ` Salman Qazi
2020-02-07 2:07 ` Ming Lei
2020-02-07 15:26 ` Bart Van Assche [this message]
2020-02-07 18:45 ` Salman Qazi
2020-02-07 19:04 ` Salman Qazi
2020-02-07 20:19 ` Bart Van Assche
2020-02-07 20:37 ` Salman Qazi
2020-04-20 16:42 ` Doug Anderson
2020-04-23 20:13 ` Jesse Barnes
2020-04-23 20:34 ` Jens Axboe
2020-04-23 20:40 ` Salman Qazi
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