linux-kernel - Re: [PATCH 5/5] blkcg: remove blkio_group->stats

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Message-ID: <20120309171523.GB7746@redhat.com>
Date:	Fri, 9 Mar 2012 12:15:23 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, dpshah@...gle.com,
	ctalbott@...gle.com, rni@...gle.com
Subject: Re: [PATCH 5/5] blkcg: remove blkio_group->stats_lock

On Thu, Mar 08, 2012 at 10:54:00AM -0800, Tejun Heo wrote:
> With recent plug merge updates, all non-percpu stat updates happen
> under queue_lock making stats_lock unnecessary to synchronize stat
> updates.  The only synchronization necessary is stat reading, which
> can be done using u64_stats_sync instead.
> 
> This patch removes blkio_group->stats_lock and adds
> blkio_group_stats->syncp for reader synchronization.
> 

Good to see stat_lock going away. That lock was confusing as we were doing
updates under queue_lock anyway. One less lock to think about now.

This stat code is messy though. All time related stat, maintaining flags,
dividing stats between read/write, sync/async. I think we are maintaining
way too much of stat. (/me wished there was a way to get rid of some of
the stats and make code simpler).

Thanks
Vivek
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