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

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Message-ID: <20070503194827.GA10423@elte.hu>
Date:	Thu, 3 May 2007 21:48:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ting Yang <tingy@...umass.edu>
Cc:	linux-kernel@...r.kernel.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 !

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.

	Ingo
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