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

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Message-ID: <52138C5E.4060705@linux.intel.com>
Date:	Tue, 20 Aug 2013 08:33:50 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Fernando Luis Vázquez Cao 
	<fernando_b1@....ntt.co.jp>, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

On 8/20/2013 8:29 AM, Frederic Weisbecker wrote:

>>
>> Of course, if we can get away with completely removing all of that
>> (which I think Arjan suggested was a real possibility) then that would
>> be ever so much better still :-)
>
> Would be lovely. But I don't know much about cpufreq, I hope somebody who's
> familiar with that code can handle this. Then once there are no more users
> of get_cpu_iowait_sleep_time() I can simply zap and clean the tick/time related
> code.

it's just doing the "idle = 100 - busy% - iowait%" calculation.
(with the later part only for Intel cpus iirc)

in a perfect world the scheduler would be doing that calculation in the first place ;-)

removing the later part will impact performance some on specific workloads,
but most Intel cpus that this applies to should not be using cpufreq anymore
anyway.


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