linux-kernel - Re: [PATCH] sched.c: Be a bit more conservative in SMP

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Date:	Wed, 20 Sep 2006 09:42:53 +0200
From:	Ludovic Drolez <ldrolez@...box.com>
To:	Antonio Vargas <windenntw@...il.com>
CC:	linux-kernel@...r.kernel.org, subdino2004@...oo.fr
Subject: Re: [PATCH] sched.c: Be a bit more conservative in SMP

Antonio Vargas wrote:
> A variant on this theme would be (not tested or somewhat, just a
> random idea for considering):
> 
> 1. find if the process is a cpu-hog, if not then ignore
> 
> 2. find somehow how much time has this process on it's current cpu
> 
> 3. then, instead of always substracting 1 from th current load on the
> current cpu, substract for example 1...0 when running from 0 to 60
> seconds... this way cpu hogs would only rotate slowly?
> 
> in code:
> 
> number_to_sub_from_queue_load = (256 - min(256,
> time_from_last_change_of_cpu)) >> 8;
> 
> somehow managing to get fixedpoint loadlevels on the runqueues would
> make this work better....
> 

Yes ! That might be a better idea !
In fact, I tested the 1st patch on our cluster (Finite elements computing on 8 
CPUs):
- Under Windows: 875 seconds
- Linux 2.6.16 : 1019 s
- Linux 2.6.16 + manual taskset : 842 s
- Linux 2.6.16 + Vincent's patch : 1373 s  :-(

If you find time to write a patch, Antonio, I would be pleased to try it !

Cheers,

-- 
Ludovic DROLEZ
http://lrs.linbox.org - Free asset management software
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