Re: [patch 0/2] NOHZ vs. profile/oprofile v2

Martin Schwidefsky
2009-06-22T15:20:30Z

On Mon, 22 Jun 2009 17:05:53 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:
>
> > On Mon, 22 Jun 2009 16:41:10 +0200
> > Ingo Molnar <mingo@elte.hu> wrote:
> >
> > > Hm, this is rather ugly. Why not use hrtimers like 'perf' does when
> > > it fallback-samples based on the timer tick?
> > >
> > > That method has three advantages:
> > >
> > > - no weird hookery needed
> > > - resolution can go far beyond HZ
> > > - it is evidently dynticks-safe
> >
> > Hmm, if we replace the HZ based oprofile tick with an hrtimer we
> > should add an interface to configure the sample interval as well,
> > no? Otherwise we just replace one timer event (HZ) with another
> > (hrtimer).
>
> Even if the hrtimer is set with a 1/HZ period it's a better
> solution, as it's dynticks safe without invasive changes.

Ok, but the patch will be quite big. All the profile_tick() calls from
the architecture files will have to be removed. And if we really want
to keep things separate there will be two sets of per-cpu hrtimer,
one for the old style profiler and one for oprofile. Any preference
for the user space interface to set the sample rate? A sysctl?