linux-kernel - Re: Question about fair schedulers

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Date:	Wed, 27 Jun 2007 16:28:21 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Alberto Gonzalez <info@...bu.es>
CC:	Tom Spink <tspink@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question about fair schedulers

Alberto Gonzalez wrote:
> On Saturday 23 June 2007, Tom Spink wrote:
>> Alberto,
>>
>> If you're feeling adventurous, grab the latest kernel and patch it
>> with Ingo's scheduler: CFS.
>>
>> You may be pleasantly surprised.
> 
> Thanks, I might if I have to courage to patch and compile my own kernel :)
> 
> However, I'd also need to change all my applications to set them with the 
> right priority to see the good results, so I think I might just wait until it 
> lands in mainline.

In general not the case. I generally don't diddle my priorities, there's 
rarely a need.
> 
> Just to check if I understood everything correctly:
> 
> The mainline scheduler tries to be smart and guess the priority of each task, 
> and while it mostly hits the nail right in the head, sometimes it hits you 
> right in the thumb.
> 
> Fair schedulers, on the contrary, forget about trying to be smart and just 
> care about being fair, leaving the priority settings to where they belong: 
> applications.
> 
> Is this more or less correct?

Incomplete. The CFS scheduler seems to do better with latency, so you 
may get less CPU to a process but it doesn't wind up waiting a long time 
to get a fair share. So it "feels better" without micro tuning.

Face it, if you have more jobs than CPU no scheduler is going to make 
you really happy.
> 
> Alberto.
> 


-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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