Re: [RFC/PATCH] perf report: Support latency profiling in system-wide mode

[Namhyung Kim <namhyung@kernel.org>]

On Tue, May 06, 2025 at 08:46:20AM +0200, Dmitry Vyukov wrote:
> On Tue, 6 May 2025 at 08:43, Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Tue, May 06, 2025 at 07:55:25AM +0200, Dmitry Vyukov wrote:
> > > Where does the patch check that this mode is used only for system-wide profiles?
> > > Is it that PERF_SAMPLE_CPU present only for system-wide profiles?
> >
> > Basically yes, but you can use --sample-cpu to add it.
> 
> Are you sure? --sample-cpu seems to work for non-system-wide profiles too.

Yep, that's why I said "Basically".  So it's not 100% guarantee.

We may disable latency column by default in this case and show warning
if it's requested.  Or we may add a new attribute to emit sched-switch
records only for idle tasks and enable the latency report only if the
data has sched-switch records.

What do you think?

Thanks,
Namhyung

> 
> > In util/evsel.c::evsel__config():
> >
> >         if (target__has_cpu(&opts->target) || opts->sample_cpu)
> >                 evsel__set_sample_bit(evsel, CPU);