linux-kernel - Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr

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Date:	Sun, 12 Sep 2010 11:14:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Lindgren <tony@...mide.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [RFC patch 1/2] sched: dynamically adapt granularity with
 nr_running

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.
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