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Subject: Re: [RFC patch 1/2] sched: dynamically adapt granularity with
 nr_running
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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Date: Sun, 12 Sep 2010 11:14:27 +0200
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On Sun, 2010-09-12 at 11:06 +0200, Peter Zijlstra wrote:
>  * is slice length, + is period length
> 
> Patch (sched_latency = 10, sched_min_gran = 10/3)
> 
> 
> 30 |                             +
>    |
>    |
>    |                          +
>    |
>    |
>    |
>    |
>    |
>    |
> 20 |
>    |
>    |
>    |
>    |
>    |
>    |
>    |
>    |
>    |
> 10 |  *  +  +  +  +  +  +  +
>    |
>    |
>    |
>    |
>    |     *
>    |
>    |        *  *              *  *  *  *  *  *
>    |              *  *
>    |                    *  *
> 0  +---------------------------------------------------------
>    0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 


Vertical is time , horz is nr_running.


Note how things fall of a cliff when nr_running goes from 8 to 9. Andrew
usually kicks people in the teeth for phase change behaviour.