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SubjectRe: CFS review
On Thu, Aug 02, 2007 at 08:57:47PM -0700, Arjan van de Ven wrote:
> 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...

Indeed. I'm just pointing out that not having TSC, fast HZ, no-HZ
mode, or high-res timers should not be treated as an unusual
circumstance. That's a PC-centric view.

--
Mathematics is the supreme nostalgia of our time.
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