linux-kernel - Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

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Message-ID: <20130819111556.GF24092@twins.programming.kicks-ass.net>
Date:	Mon, 19 Aug 2013 13:15:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

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.


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