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

Ingo Molnar
2009-06-22T15:40:47Z

* Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> On Mon, 22 Jun 2009 17:29:37 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
>
> >
> > * Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:
> >
> > > 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. [...]
> >
> > Hey, that's a bonus :)
>
> It would remove some oddball code :-)
>
> > > [...] 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?
> >
> > I dont think we want to keep things separate. Regarding old-style
> > profiler, does anyone still use it? There's now a superior in-tree
> > replacement for it, so we could phase it out.
>
> Well, for my part I won't miss it. But to be able to remove the
> profile_tick() calls from the architectures I either have to rip
> out the old profiler now, or adapt it to use hrtimer as well.

Do we _have to_ touch it so widely right now? We could start with a
deprecation warning in this cycle. Once it's deprecated we can
remove all those calls.

Ingo