From: Christoph Hellwig <hch@infradead.org>
To: Jens Axboe <axboe@fb.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org, jbacik@fb.com,
Ming Lei <ming.lei@canonical.com>
Subject: Re: [PATCH 2/2] blk-mq: add flag for drivers wanting blocking ->queue_rq()
Date: Thu, 22 Sep 2016 07:59:22 -0700 [thread overview]
Message-ID: <20160922145922.GB1800@infradead.org> (raw)
In-Reply-To: <1474555980-2787-3-git-send-email-axboe@fb.com>
On Thu, Sep 22, 2016 at 08:53:00AM -0600, Jens Axboe wrote:
> If a driver sets BLK_MQ_F_BLOCKING, it is allowed to block in its
> ->queue_rq() handler. For that case, blk-mq ensures that we always
> calls it from a safe context.
First can you provide a more useful defintion of blocking? Lots of current
drivers will already block in ->queue_rq, mostly to allocate memory.
Second we looked at something similar a few times ago, mosty notably
when converting loop and rbd, and came to the conclusion that
performance sucks when we only have that single per-hctx work struct
for a busy device. I think Ming has done a lot of the benchmarking,
so I've added him to Cc.
next prev parent reply other threads:[~2016-09-22 14:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-22 14:52 [PATCH 0/2]: Add option for async ->queue_rq Jens Axboe
2016-09-22 14:52 ` [PATCH 1/2] blk-mq: get rid of manual run of queue with __blk_mq_run_hw_queue() Jens Axboe
2016-09-22 14:56 ` Christoph Hellwig
2016-09-22 18:56 ` Christoph Hellwig
2016-09-22 20:29 ` Jens Axboe
2016-09-23 21:59 ` Sagi Grimberg
2016-09-23 21:56 ` Sagi Grimberg
2016-09-22 14:53 ` [PATCH 2/2] blk-mq: add flag for drivers wanting blocking ->queue_rq() Jens Axboe
2016-09-22 14:59 ` Christoph Hellwig [this message]
2016-09-22 15:03 ` Jens Axboe
2016-09-22 15:12 ` Christoph Hellwig
2016-09-22 15:17 ` Jens Axboe
2016-09-23 1:43 ` Ming Lei
2016-09-23 2:44 ` Josef Bacik
2016-09-23 1:35 ` Ming Lei
2016-09-22 15:04 ` Josef Bacik
2016-09-22 18:01 ` [PATCH 0/2]: Add option for async ->queue_rq Josef Bacik
2016-09-28 0:25 ` Bart Van Assche
2016-09-28 16:43 ` Omar Sandoval
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