linux-kernel - Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO performance

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Message-ID: <4e5e476b0911090529g6ba93a9o91cfc1b15d7497d1@mail.gmail.com>
Date:	Mon, 9 Nov 2009 14:29:17 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, lenb@...nel.org,
	mingo@...e.hu, yanmin_zhang@...ux.intel.com, jens.axboe@...cle.com,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Subject: Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO performance

On Sun, Nov 8, 2009 at 11:30 PM, Arjan van de Ven <arjan@...radead.org> wrote:
> On Sun, 8 Nov 2009 22:59:43 +0100
> I think we all agree that long term polling is bad ;-)
> (even though we use rep nop in the polling loop which is also a HT
> yield).
>
> There's just the very short sleeps (where short is "single digit usecs")
> where the rules are slightly different.
>
>> > this check is supposed to catch the known timer cases; those
>> > are rather accurate in prediction
>>
>> Unfortunately, I have seen polling residency times > 1ms, so it must
>> not be so accurate.
>
> well the question is... is this a measurement error or an error in
> when polling is chosen.
> We obviously need to fix it whatever it is, but... first need to chase
> down really which it is.

Any suggestion on how to check?
Clocksource is hpet, and I have CONFIG_SCHED_HRTICK=y, so the
granularity should not be a problem.

Corrado
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