lkml.org 
[lkml]   [2007]   [Aug]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: CFS review
From
Date
On Fri, 2007-08-03 at 06:18 +0200, Willy Tarreau wrote:
> 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...
>
> Well, at least we're able to *measure* that task 'l' used 3.3% and
> that tasks 'lt' used 32%.

It's not measured if you use jiffies level stuff. It's at best sampled!

> If we're able to measure it, then that's
> already fine enough to be able to adjust future timeslices credits.
> Granted it may be rough for small periods (a few jiffies), but it
> should be fair for larger periods. Or at least it should *report*

but the testcase here uses a LOT shorter time than jiffies... not "a few
jiffies".

--
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-08-03 06:35    [W:0.347 / U:18.592 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site