Re: [PATCH v2] perf metrics: Add literal for system TSC frequency

Peter Zijlstra
2022-05-28T15:40:48Z

On Sat, May 28, 2022 at 07:50:40AM -0700, Ian Rogers wrote:
> On Sat, May 28, 2022 at 7:02 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, May 27, 2022 at 07:54:19AM -0700, Andi Kleen wrote:
> >
> > > > This all seems bonghits inspired... and perf actually does expose the
> > > > tsc frequency. What do you think is in perf_event_mmap_page::time_* ?
> > >
> > >
> > > That's not really available to perf stat, which is the primary metrics user.
> >
> > Why not? You can mmap any perf-fd (even software events) and these
> > fields should be filled out.
> >
> > It should work on any x86 CPU that has a TSC. The only caveat is that
> > the kernel must not have marked the TSC unstable.
> >
> > It could even work for virt -- all you need is for virt to use
> > native_sched_clock() instead of the paravirt nonsense.
>
> It will at least fail if inherit is enabled, no?

For per-task events, yes, I suppose it will. I'd forgotten about that
restriction on perf_mmap() :/