Messages in this thread Patch in this message | | | Date | Wed, 9 Nov 2016 10:59:27 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf tools pt: Remove obsolete paragraph in intel-pt.c |
| |
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 <ak@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.
| |