From: Christoph Hellwig <hch@infradead.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] blk-mq: only run the hardware queue if IO is pending
Date: Fri, 10 Nov 2017 09:29:57 -0800 [thread overview]
Message-ID: <20171110172957.GA29446@infradead.org> (raw)
In-Reply-To: <b1c29434-929d-a8aa-7181-b0b90607ede1@kernel.dk>
On Fri, Nov 10, 2017 at 09:12:18AM -0700, Jens Axboe wrote:
> Currently we are inconsistent in when we decide to run the queue. Using
> blk_mq_run_hw_queues() we check if the hctx has pending IO before
> running it, but we don't do that from the individual queue run function,
> blk_mq_run_hw_queue(). This results in a lot of extra and pointless
> queue runs, potentially, on flush requests and (much worse) on tag
> starvation situations. This is observable just looking at the top
> output, with lots of kworkers active. For the !async runs, it just adds
> to the CPU overhead of blk-mq.
>
> Move the has-pending check into the run function instead of having
> callers do it.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Do we even still need the blk_mq_hctx_has_pending helper at all?
Except for that this looks fine to me:
Reviewed-by: Christoph Hellwig <hch@lst.de>
next prev parent reply other threads:[~2017-11-10 17:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-10 16:12 [PATCH] blk-mq: only run the hardware queue if IO is pending Jens Axboe
2017-11-10 17:29 ` Christoph Hellwig [this message]
2017-11-10 17:31 ` Jens Axboe
2017-11-10 17:34 ` Christoph Hellwig
2017-11-10 17:35 ` Jens Axboe
2017-11-10 22:28 ` Omar Sandoval
2017-11-10 22:31 ` Jens Axboe
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