linux-kernel - Re: [patch] CFS scheduler, -v7

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Message-ID: <20070503195738.GX31925@holomorphy.com>
Date:	Thu, 3 May 2007 12:57:38 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Ting Yang <tingy@...umass.edu>, linux-kernel@...r.kernel.org,
	davidel@...ilserver.org
Subject: Re: [patch] CFS scheduler, -v7

* Ting Yang <tingy@...umass.edu> wrote:
>> then how much time is needed for "curr" to build a 2 * 32 difference 
>> on fair_key, with every 1 ms it updates fair_key by 1/32 ?  2 * 32 * 
>> 32 !

On Thu, May 03, 2007 at 09:48:27PM +0200, Ingo Molnar wrote:
> yes - but the "*32" impacts the rescheduling granularity, the "/32" 
> impacts the speed of how the key moves. So the total execution speed of 
> the nice -10 task is still "*32" of a nice 0 task - it's just that not 
> only it gets 32 times more CPU time, it also gets it at 32 times larger 
> chunks at once. But the rescheduling granularity does _not_ impact the 
> CPU share the task gets, so there's no quadratic effect.
> but this is really simple to test: boot up CFS, start two infinite 
> loops, one at nice 0 and one at nice +10 and look at it via "top" and 
> type 's 60' in top to get a really long update interval for precise 
> results. You wont see quadratically less CPU time used up by the nice 
> +10 task, you'll see it getting the intended 1/32 share of CPU time.

Davide has code to test this more rigorously. Looks like I don't need
to do very much to get a nice test going at all, besides fiddling with
options parsing and maybe a few other things.


-- wli
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