linux-kernel - Re: [PATCH 2/6] blkcg: add blkg_[rw]stat->aux_cnt and replace cfq_group->dead

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Message-ID: <20150626134525.GB14803@redhat.com>
Date:	Fri, 26 Jun 2015 09:45:25 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, avanzini.arianna@...il.com,
	kernel-team@...com
Subject: Re: [PATCH 2/6] blkcg: add blkg_[rw]stat->aux_cnt and replace
 cfq_group->dead_stats with it

On Fri, Jun 26, 2015 at 09:35:40AM -0400, Tejun Heo wrote:
> On Fri, Jun 26, 2015 at 09:27:02AM -0400, Vivek Goyal wrote:
> > On Thu, Jun 25, 2015 at 05:38:53PM -0400, Tejun Heo wrote:
> > 
> > [..]
> > > It's planned that the core stats will be moved to blkcg_gq, so we want
> > > to move the mechanism for keeping track of the stats of dead children
> > > from cfq to blkcg core.  This patch adds blkg_[rw]stat->aux_cnt which
> > > are atomic64_t's keeping track of auxiliary counts which are excluded
> > > when reading local counts but included for recursive.
> > 
> > Hi Tejun,
> > 
> > So aux_cnt is atomic64_t as updation is not the hot path hence there is
> > not much value in keeping it as per cpu?
> 
> I'm not following.  aux_cnt isn't per-cpu.

I was just curious that why aux_cnt is different from rest of the stats.
(It is atomic64_t while others are not).

Thanks
Vivek
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