Em Wed, Nov 09, 2016 at 04:01:12PM +0200, Adrian Hunter escreveu:
> On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
> >> Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
> >>> From: Andi Kleen <a...@linux.intel.com>
> >>>
> >>> Since the unprivileged sched switch event was added in perf,
> >>> PT doesn't need need perf_event_paranoid=-1 anymore for
> >>> per cpu decoding. So remove the obsolete paragraph in
> >>> the documentation.
> >>
> >> Thanks for pointing that out, I'll do something slightly different tho,
> >> pointing out that from kernel X.Y.Z, when the unprivileged
> >> PERF_RECORD_SWITCH metadata event was introduced, this is no longer an
> >> issue, having to be considered only on older kernels.
> >
> > It ended up as:
> >
> > diff --git a/tools/perf/Documentation/intel-pt.txt
> > b/tools/perf/Documentation/intel-pt.txt
> > index c6c8318e38a2..4d12db118476 100644
> > --- a/tools/perf/Documentation/intel-pt.txt
> > +++ b/tools/perf/Documentation/intel-pt.txt
> > @@ -546,6 +546,18 @@ mode by using the --per-thread option.
> > Privileged vs non-privileged users
> > ----------------------------------
> >
> > +The v4.2 kernel introduced support for a context switch metadata event,
> > +PERF_RECORD_SWITCH, which allows unprivileged users to see when their
> > processes
> > +are scheduled out and in, just not by whom, which is left for the
> > +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide
> > context,
> > +which in turn requires CAP_SYS_ADMIN.
> > +
> > +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate
> > context
> > +switches") commit, that introduces these metadata events for further info.
> > +
> > +When working with kernels < v4.2, the following considerations must be
> > taken,
> > +as the sched:sched_switch tracepoints will be used to receive such
> > information:
> > +
> > Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged
> > users
> > have memory limits imposed upon them. That affects what buffer sizes they
> > can
> > have as outlined above.
>
> Maybe put that last paragraph about memory limits above the new text.
Ok, as it is not affected by the new text, thanks.
- Arnaldo
