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Date: Mon, 19 Aug 2013 13:15:56 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
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        LKML <linux-kernel@vger.kernel.org>,
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        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock
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On Mon, Aug 19, 2013 at 01:10:26PM +0200, Peter Zijlstra wrote:
> So no, if we need per-cpu iowait time we have to do A.
> 
> Since we already have atomics in the io_schedule*() paths, please
> replace those with (seq)locks. Also see if you can place the entire
> iowait accounting thing in a separate cacheline.

Also, it completely blows to have these extra atomics in the IO paths,
I'm sure that the Mega-IOP/s people would be much pleased if we could
remove these.