diff options
| author | Arnaldo Carvalho de Melo <acme@redhat.com> | 2016-11-09 11:04:05 -0300 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2016-11-11 13:18:52 -0300 |
| commit | 699c12a7cca376d16f75672f9047faa37b184eda (patch) | |
| tree | 6a68d876b73f4b981003c0264c96eb0f51862117 /tools | |
| parent | c56cb33b56c13493eeb95612f80e4dd6e35cd109 (diff) | |
perf intel-pt: Update documentation about context switch events
Since the unprivileged sched switch event was added in perf, PT doesn't
need need perf_event_paranoid=-1 anymore for per cpu decoding.
Add a note stating that that is only needed for kernels < 4.2.
Reported-by: Andi Kleen <ak@linux.intel.com>
Report-Link: http://lkml.kernel.org/r/http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Fixes: 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context switches")
Link: http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/perf/Documentation/intel-pt.txt | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt index c6c8318e38a2..b0b3007d3c9c 100644 --- a/tools/perf/Documentation/intel-pt.txt +++ b/tools/perf/Documentation/intel-pt.txt @@ -550,6 +550,18 @@ 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. +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 are not permitted to use tracepoints which means there is insufficient side-band information to decode Intel PT in per-cpu mode, and potentially workload-only @@ -564,8 +576,11 @@ sched_switch tracepoint ----------------------- The sched_switch tracepoint is used to provide side-band data for Intel PT -decoding. sched_switch events are automatically added. e.g. the second event -shown below +decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't +available. + +The sched_switch events are automatically added. e.g. the second event shown +below: $ perf record -vv -e intel_pt//u uname ------------------------------------------------------------ |