* Peter Zijlstra <pet...@infradead.org> wrote:
> On Fri, May 10, 2013 at 12:18:23PM +0200, Ingo Molnar wrote:
> >
> > * Peter Zijlstra <pet...@infradead.org> wrote:
> >
> > > > so you mean just detect that by opening events with increasing precise
> > > > and see how far we could get.. could be I guess, though the 'precise'
> > > > sysfs attribute seems more fit to me
> > >
> > > The other way around, start at ppp end at !p, then use the one that
> > > worked.
> >
> > Really, instead of this silly 'probing until it works' notion, how about
> > the radical idea that we pass to the kernel our request, and the kernel
> > fulfills our wish to the best of its ability?
> >
> > This could be done as a new PERF_COUNT_HW_CPU_CYCLES_PRECISE event, to
> > which tooling could migrate, without changing existing semantics.
> >
> > The problem with the complex probing is that it's totally unnecessary
> > complexity that results from lack of passing the right information to the
> > kernel. Forcing that will only hinder user-space adoption of our precise
> > profiling facilities.
>
> The part I have trouble with is that its a vague request and you'll get
> a vague answer.
PERF_COUNT_HW_CPU_CYCLES_PRECISE is not a vague request at all: it means
'get me the most precise cycles profiling available on this system'.
Thanks,
Ingo
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