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Subject: Re: CFS review
From: Arjan van de Ven <arjan@infradead.org>
To: Matt Mackall <mpm@selenic.com>
Cc: Ingo Molnar <mingo@elte.hu>, Roman Zippel <zippel@linux-m68k.org>,
       Mike Galbraith <efault@gmx.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
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Organization: Intel International BV
Date: Thu, 02 Aug 2007 20:57:47 -0700
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On Thu, 2007-08-02 at 22:04 -0500, Matt Mackall wrote:
> On Wed, Aug 01, 2007 at 01:22:29PM +0200, Ingo Molnar wrote:
> > 
> > * Roman Zippel <zippel@linux-m68k.org> wrote:
> > 
> > > [...] e.g. in this example there are three tasks that run only for 
> > > about 1ms every 3ms, but they get far more time than should have 
> > > gotten fairly:
> > > 
> > >  4544 roman     20   0  1796  520  432 S 32.1  0.4   0:21.08 lt
> > >  4545 roman     20   0  1796  344  256 R 32.1  0.3   0:21.07 lt
> > >  4546 roman     20   0  1796  344  256 R 31.7  0.3   0:21.07 lt
> > >  4547 roman     20   0  1532  272  216 R  3.3  0.2   0:01.94 l
> > 
> > Mike and me have managed to reproduce similarly looking 'top' output, 
> > but it takes some effort: we had to deliberately run a non-TSC 
> > sched_clock(), CONFIG_HZ=100, !CONFIG_NO_HZ and !CONFIG_HIGH_RES_TIMERS.
> 
> ..which is pretty much the state of play for lots of non-x86 hardware.

question is if it's significantly worse than before. With a 100 or
1000Hz timer, you can't expect perfect fairness just due to the
extremely rough measurement of time spent...