linux-kernel - Re: [PATCHSET] blkcg: unify blkgs for different policies

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Date:	Thu, 2 Feb 2012 12:36:09 -0800
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
Subject: Re: [PATCHSET] blkcg: unify blkgs for different policies

Hello,

On Thu, Feb 02, 2012 at 02:29:58PM -0500, Vivek Goyal wrote:
> On Wed, Feb 01, 2012 at 01:19:05PM -0800, Tejun Heo wrote:
> 
> [..]
> > 
> > * use unified stats updated under queue lock and drop percpu stats
> >   which should fix locking / context bug across percpu allocation.
> 
> Does that mean that stat updation will happen under queue lock even if
> there are no throttling rules? That will introduce extra queue lock on
> fast path those who have throttling compiled in but are not using (common
> case for distributions).

No, I don't think extra locking would be necessary at all.  We end up
grabbing queue_lock anyway.  It's just the matter of where to update
the stats.

Thanks.

-- 
tejun
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