linux-kernel - Re: CFS not suitable for desktop computers

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Message-Id: <1241597020.11251.82.camel@twins>
Date:	Wed, 06 May 2009 10:03:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nico Schümann <spam@...o22.de>
Cc:	linux-kernel@...r.kernel.org, Mike Galbraith <efault@....de>
Subject: Re: CFS not suitable for desktop computers

On Mon, 2009-05-04 at 17:16 +0200, Nico Schümann wrote: 
> Thank you Ray Lee and Mike Galbraith for your responses, I ran the 
> script and attached its gathered information.
> 
> Mike Galbraith wrote:
> > How hard is hard?  Can you describe the loads you're having trouble
> > with, and the hardware you're running them on?
> >
> >   
> I could reproduce "hard" load by just compiling the linux kernel, make 
> -j3 while reading mails with Thunderbird, which is not that hard 
> foreground load. Thunderbird starts reacting really slowly while compiling.

Right, such a load will leave your thunderbird about 25% of the cpu. I
think its fair to expect it to be slower, but it should still be
workable.

I used to test CFS on my 1.2GHz laptop with 512M and a make -j5. That
would result in a slow but steady system. With steady I mean the latency
was pretty constant.

The O(1) scheduler would utterly mess this up, it would be fast, until
the desktop bloat took enough cpu time and then it would starve a while,
etc..

The thing is, we really cannot go about guessing, its too easy to guess
wrong. If you know its a background task, nice it.

alias make='nice make'

and you're done.
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