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 <[email protected]> >>> >>> 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.
