Re: [PATCH 2/7] Simple Performance Counters: x86_64 support

Andi Kleen
2007-08-01T18:57:52Z

On Wed, Aug 01, 2007 at 11:45:39AM -0700, Christoph Lameter wrote:
> On Wed, 1 Aug 2007, Andi Kleen wrote:
>
> > > It is certainly interesting to compare alternative ways of handling the
> > > instruction streams by various processors or models of processors.
> >
> > Well you have to do a lot more work then to handle instable TSCs then.
>
> I have been using this for 2 years. It works fine for my purposes.

That might be on your systems, but for a mainline submission the
standards are higher.

>
> > In particular the frequencies can be different between CPUs, they
> > change (which you can catch with cpufreq notifiers) and during the
> > cpufreq change period they're instable (as in you can't tell for
> > some time which frequency they're currently running at and they
> > might be running immediate frequencies)
>
> Well then simply make sure that they do not change while you measure.

That would be a merge blocker in my opinion. Suitable for local
hacks, but nothing we want in tree.

-Andi