linux-kernel - Re: [PATCH 07/11] blkcg: make request

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Message-ID: <20120413204710.GF12233@google.com>
Date:	Fri, 13 Apr 2012 13:47:10 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH 07/11] blkcg: make request_queue bypassing on allocation

On Fri, Apr 13, 2012 at 04:44:46PM -0400, Vivek Goyal wrote:
> On Fri, Apr 13, 2012 at 01:37:26PM -0700, Tejun Heo wrote:
> 
> [..]
> > blk_cleanup_queue() doesn't use blk_queue_bypass_start() to enter
> > bypass mode.
> 
> Oh now elevator_exit() has been moved into blk_release_queue(). But
> problem will still be there, isn't it? During driver init, most likely driver
> is holding last reference of the queue and blk_release_queue() will be called
> in the context of blk_cleanup_queue() causing the overhead?

Hmmm?  blk_cleanup_queue() will put the queue into bypassing mode
without going through synchronize_rcu() and all the following
bypassing operations just inc/decs bypass_depth without any draining
operation.

Thanks.

-- 
tejun
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