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:
> > +++ 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, adding your Acked-by, it now stands as, please ack:
commit c955ced680270b95a3de6a2434311befaeaea948
Author: Arnaldo Carvalho de Melo <a...@redhat.com>
Date: Wed Nov 9 11:04:05 2016 -0300
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 <a...@linux.intel.com>
Report-link:
http://lkml.kernel.org/r/http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi...@git.kernel.org
Acked-by: Adrian Hunter <adrian.hun...@intel.com>
Fixes: 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
switches")
Link: http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi...@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com>
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
------------------------------------------------------------
