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SubjectRe: [PATCH v6 7/7] perf intel-pt: Add brief documentation for PEBS via Intel PT
Em Tue, Aug 13, 2019 at 05:05:46PM +0300, Alexander Shishkin escreveu:
> Arnaldo Carvalho de Melo <acme@redhat.com> writes:
>
> > Em Tue, Aug 06, 2019 at 11:46:06AM +0300, Alexander Shishkin escreveu:
> >> From: Adrian Hunter <adrian.hunter@intel.com>
> >>
> >> Document how to select PEBS via Intel PT and how to display synthesized
> >> PEBS samples.
> >>
> >> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> >> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> >> ---
> >> tools/perf/Documentation/intel-pt.txt | 15 +++++++++++++++
> >> 1 file changed, 15 insertions(+)
> >>
> >> diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> >> index 50c5b60101bd..8dc513b6607b 100644
> >> --- a/tools/perf/Documentation/intel-pt.txt
> >> +++ b/tools/perf/Documentation/intel-pt.txt
> >> @@ -919,3 +919,18 @@ amended to take the number of elements as a parameter.
> >>
> >> Note there is currently no advantage to using Intel PT instead of LBR, but
> >> that may change in the future if greater use is made of the data.
> >> +
> >> +
> >> +PEBS via Intel PT
> >> +=================
> >> +
> >> +Some hardware has the feature to redirect PEBS records to the Intel PT trace.
> >> +Recording is selected by using the aux-output config term e.g.
> >> +
> >> + perf record -c 10000 -e cycles/aux-output/ppp -e intel_pt/branch=0/ uname
> >> +
> >> +Note that currently, software only supports redirecting at most one PEBS event.
> >
> > So, with these patches, but not the kernel ones I end up getting:
> >
> > [root@quaco ~]# perf record -c 10000 -e cycles/aux-output/ppp -e intel_pt/branch=0/ uname
>
> FWIW, the correct command line for that would have the two events
> grouped and intel_pt be the group leader.

I've just blindly followed the provided documentation :)

So you say I should have tried this instead:

# perf record -c 10000 -e '{intel_pt/branch=0/,cycles/aux-output/ppp}' uname
Error:
The 'aux_output' feature is not supported, update the kernel.
#

Or with leader sampling?

# perf record -c 10000 -e '{intel_pt/branch=0/,cycles/aux-output/ppp}:S' uname
Error:
The 'aux_output' feature is not supported, update the kernel.
#

This is with the patch at the end of this message and without the kernel counterpart.

- Arnaldo

commit 58c5a9772d88f5dead1e561f6323f9f355625caa
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date: Tue Aug 13 11:06:38 2019 -0300

perf evsel: Provide meaningful warning when trying to use 'aux_output' on older kernels

Just like we do with the 'write_backwards' feature:

Before:

# perf record -c 10000 -e cycles/aux-output/ppp -e intel_pt/branch=0/ uname
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cycles/aux-output/ppp).
/bin/dmesg | grep -i perf may provide additional information.

#

After:

# perf record -c 10000 -e cycles/aux-output/ppp -e intel_pt/branch=0/ uname
Error:
The 'aux_output' feature is not supported, update the kernel.
#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-wgjsjroe1e150c0metgwmqwd@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 6f08aea4f108..0b3b5af33954 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1738,7 +1738,8 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
int pid = -1, err;
enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;

- if (perf_missing_features.write_backward && evsel->core.attr.write_backward)
+ if ((perf_missing_features.write_backward && evsel->core.attr.write_backward) ||
+ (perf_missing_features.aux_output && evsel->core.attr.aux_output))
return -EINVAL;

if (cpus == NULL) {
@@ -1912,7 +1913,11 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
* Must probe features in the order they were added to the
* perf_event_attr interface.
*/
- if (!perf_missing_features.bpf_event && evsel->core.attr.bpf_event) {
+ if (!perf_missing_features.aux_output && evsel->core.attr.aux_output) {
+ perf_missing_features.aux_output = true;
+ pr_debug2("Kernel has no attr.aux_output support, bailing out\n");
+ goto out_close;
+ } else if (!perf_missing_features.bpf_event && evsel->core.attr.bpf_event) {
perf_missing_features.bpf_event = true;
pr_debug2("switching off bpf_event\n");
goto fallback_missing_features;
@@ -2926,6 +2931,8 @@ int perf_evsel__open_strerror(struct evsel *evsel, struct target *target,
return scnprintf(msg, size, "clockid feature not supported.");
if (perf_missing_features.clockid_wrong)
return scnprintf(msg, size, "wrong clockid (%d).", clockid);
+ if (perf_missing_features.aux_output)
+ return scnprintf(msg, size, "The 'aux_output' feature is not supported, update the kernel.");
break;
default:
break;
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 8a316dd54cd0..9cd6e3ae479a 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -184,6 +184,7 @@ struct perf_missing_features {
bool group_read;
bool ksymbol;
bool bpf_event;
+ bool aux_output;
};

extern struct perf_missing_features perf_missing_features;
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