From: Jens Axboe <axboe@kernel.dk>
To: Salman Qazi <sqazi@google.com>, Ming Lei <ming.lei@redhat.com>,
Bart Van Assche <bvanassche@acm.org>,
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 v3] block: Limit number of items taken from the I/O scheduler in one go
Date: Fri, 24 Apr 2020 09:17:23 -0600 [thread overview]
Message-ID: <8998250d-4945-9efd-6936-07e55d505e25@kernel.dk> (raw)
In-Reply-To: <20200424150321.38617-1-sqazi@google.com>
On 4/24/20 9:03 AM, Salman Qazi wrote:
> Flushes bypass the I/O scheduler and get added to hctx->dispatch
> in blk_mq_sched_bypass_insert. This can happen while a kworker is running
> hctx->run_work work item and is past the point in
> blk_mq_sched_dispatch_requests where hctx->dispatch is checked.
>
> The blk_mq_do_dispatch_sched call is not guaranteed to end in bounded time,
> because the I/O scheduler can feed an arbitrary number of commands.
>
> Since we have only one hctx->run_work, the commands waiting in
> hctx->dispatch will wait an arbitrary length of time for run_work to be
> rerun.
>
> A similar phenomenon exists with dispatches from the software queue.
>
> The solution is to poll hctx->dispatch in blk_mq_do_dispatch_sched and
> blk_mq_do_dispatch_ctx and return from the run_work handler and let it
> rerun.
Applied for 5.8, thanks.
--
Jens Axboe
next prev parent reply other threads:[~2020-04-24 15:17 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 15:03 [PATCH v3] block: Limit number of items taken from the I/O scheduler in one go Salman Qazi
2020-04-24 15:17 ` Jens Axboe [this message]
2020-04-24 15:39 ` Christoph Hellwig
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