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From: Tejun Heo <tj@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH block/for-3.18/core] blk-mq: start q->mq_usage_counter in atomic mode
Date: Wed, 24 Sep 2014 13:33:52 -0400	[thread overview]
Message-ID: <20140924173352.GC29067@mtj.dyndns.org> (raw)
In-Reply-To: <20140923060812.GH11740@mtj.dyndns.org>

On Tue, Sep 23, 2014 at 02:08:12AM -0400, Tejun Heo wrote:
> From 83b06f4fc6ca2f7f3d706a168b71c248bdada668 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@kernel.org>
> Date: Tue, 23 Sep 2014 01:58:34 -0400
> 
> blk-mq uses percpu_ref for its usage counter which tracks the number
> of in-flight commands and used to synchronously drain the queue on
> freeze.  percpu_ref shutdown takes measureable wallclock time as it
> involves a sched RCU grace period.  This means that draining a blk-mq
> takes measureable wallclock time.  One would think that this shouldn't
> matter as queue shutdown should be a rare event which takes place
> asynchronously w.r.t. userland.

Applied to percpu/for-3.18 on top of the klude, its revert and the
required percpu_ref changes.

Thanks.

-- 
tejun

  reply	other threads:[~2014-09-24 17:33 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-19 11:38 boot stall regression due to blk-mq: use percpu_ref for mq usage count Christoph Hellwig
2014-09-19 19:13 ` Jens Axboe
2014-09-23  5:55   ` Christoph Hellwig
2014-09-23  5:56     ` Tejun Heo
2014-09-23  5:57       ` Tejun Heo
2014-09-23  5:59       ` Christoph Hellwig
2014-09-23  6:01         ` Tejun Heo
2014-09-23  6:03           ` Tejun Heo
2014-09-23  6:09           ` Christoph Hellwig
2014-09-23  6:11             ` Tejun Heo
2014-09-23 14:57               ` Elliott, Robert (Server Storage)
2014-09-23 15:49               ` Jens Axboe
2014-09-23 19:24                 ` [PATCH block/for-3.17-fixes/core] blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe Tejun Heo
2014-09-23 19:29                   ` Jens Axboe
2014-09-23 19:48                     ` Tejun Heo
2014-09-24  8:23                   ` Christoph Hellwig
2014-09-24 14:30                     ` Jens Axboe
2014-09-24 14:33                       ` Tejun Heo
2014-09-24 14:33                         ` Jens Axboe
2014-09-24 17:20                           ` [PATCH percpu/for-3.18] Revert "blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe" Tejun Heo
2014-09-23  6:08 ` [PATCH block/for-3.18/core] blk-mq: start q->mq_usage_counter in atomic mode Tejun Heo
2014-09-24 17:33   ` Tejun Heo [this message]
2014-09-24 17:43     ` [PATCH percpu/for-3.18] blk-mq, percpu_ref: " Tejun Heo

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