From mboxrd@z Thu Jan  1 00:00:00 1970
From: fweisbec@gmail.com (Frederic Weisbecker)
Date: Fri, 22 Feb 2013 15:23:05 +0100
Subject: [PATCH 0/2] cpustat: use atomic operations to read/update stats
In-Reply-To: <1361542891.3683.6.camel@edumazet-glaptop>
References: <1361512604-2720-1-git-send-email-khilman@linaro.org>
 <1361522767.26780.44.camel@laptop>
 <20130222125019.GC17948@somewhere.redhat.com>
 <1361542150.26780.64.camel@laptop>
 <1361542891.3683.6.camel@edumazet-glaptop>
Message-ID: <20130222142302.GC18149@somewhere.redhat.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Feb 22, 2013 at 06:21:31AM -0800, Eric Dumazet wrote:
> On Fri, 2013-02-22 at 15:09 +0100, Peter Zijlstra wrote:
> > On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote:
> > > > Argh!! at what cost? 64bit atomics are like expensive. Wouldn't
> > > adding
> > > > a seqlock be saner?
> > > 
> > > Not sure. This requires a spinlock in the write side which is called
> > > from
> > > fast path like the timer interrupt.
> > 
> > A single spinlock is _way_ cheaper than a ton of cmpxchg8b()s to update
> > a few variables.
> 
> We also have include/linux/u64_stats_sync.h since 2.6.36

Interesting, we should probably use that instead.