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SubjectRe: [RFC] perf record: missing buildid for callstack modules
Hi Stephane,

On Fri, Jan 08, 2016 at 10:01:24AM -0800, Stephane Eranian wrote:
> On Thu, Jan 7, 2016 at 3:47 PM, Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> > Em Fri, Jan 08, 2016 at 07:47:03AM +0900, Namhyung Kim escreveu:
> >> On January 8, 2016 7:00:35 AM GMT+09:00, Stephane Eranian <eranian@google.com> wrote:
> >> >On Thu, Jan 7, 2016 at 1:59 PM, Arnaldo Carvalho de Melo
> >> ><acme@kernel.org> wrote:
> >> >> Em Thu, Jan 07, 2016 at 01:56:14PM -0800, Stephane Eranian escreveu:
> >> >>> Hi,
> >> >>>
> >> >>> Whenever you do:
> >> >>>
> >> >>> $ perf record -g -a sleep 10
> >> >>>
> >> >>> Perf will collect the callstack for each sample. At the end of the
> >> >>> run, perf record
> >> >>> adds the buildid for all dso with at least one sample. But when it
> >> >does this, it
> >> >>> only looks at the sampled IP and ignore the modules traversed by the
> >> >callstack.
> >> >>> That means that, it is not possible to uniquely identify the modules
> >> >executed,
> >> >>> unless they had at least one IP sample captured. But this is not
> >> >>> always the case.
> >> >>>
> >> >>> How about providing an option to perf record to force collecting
> >> >>> buildid for all IPs
> >> >>> captured in the callstack? I understand that would cost more at the
> >> >end of the
> >> >>> collection, but this would be beneficial to several monitoring
> >> >scenarios.
> >> >>
> >> >> I agree, would consider applying a patch that provides the option but
> >> >> does not do this by default.
> >> >>
> >> >I agree, not the default.
> >>
> >> Hi Stephane,
> >>
> >> Please see
> >>
> >> https://lkml.org/lkml/2015/3/22/249
> >
> >
> > Oops, Stephane, please try this, so that we can finally merge it :-\
> >
> I will try it today. However, I am a bit worried about the performance
> impact. Unless I am missing something in this approach we may end up
> looking up N times the same module if it appears in N callstacks. In
> Andi's suggested approach, there would be only one pass at the beginning
> (or the end of the run). But you could miss some modules if they are gone
> by the time you run the pass.

How about this then?

Adrian, is it ok to skip process_buildids() for the auxtrace?

Thanks,
Namhyung


diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 3a1a32f5479f..fbceb631387c 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -338,6 +338,9 @@ Options passed to clang when compiling BPF scriptlets.
Specify vmlinux path which has debuginfo.
(enabled when BPF prologue is on)

+--buildid-all::
+Record build-id of all DSOs regardless whether it's actually hit or not.
+
SEE ALSO
--------
linkperf:perf-stat[1], linkperf:perf-list[1]
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index dc4e0adf5c5b..ab18db3153a6 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -50,6 +50,7 @@ struct record {
int realtime_prio;
bool no_buildid;
bool no_buildid_cache;
+ bool buildid_all;
unsigned long long samples;
};

@@ -755,14 +756,10 @@ out_child:
file->size = lseek(perf_data_file__fd(file), 0, SEEK_CUR);

if (!rec->no_buildid) {
- process_buildids(rec);
- /*
- * We take all buildids when the file contains
- * AUX area tracing data because we do not decode the
- * trace because it would take too long.
- */
- if (rec->opts.full_auxtrace)
+ if (rec->buildid_all)
dsos__hit_all(rec->session);
+ else
+ process_buildids(rec);
}
perf_session__write_header(rec->session, rec->evlist, fd, true);
}
@@ -1138,6 +1135,8 @@ struct option __record_options[] = {
"options passed to clang when compiling BPF scriptlets"),
OPT_STRING(0, "vmlinux", &symbol_conf.vmlinux_name,
"file", "vmlinux pathname"),
+ OPT_BOOLEAN(0, "buildid-all", &record.buildid_all,
+ "Record build-id of all DSOs regardless of hits"),
OPT_END()
};

@@ -1255,6 +1254,14 @@ int cmd_record(int argc, const char **argv, const char *prefix __maybe_unused)
if (err)
goto out_symbol_exit;

+ /*
+ * We take all buildids when the file contains
+ * AUX area tracing data because we do not decode the
+ * trace because it would take too long.
+ */
+ if (rec->opts.full_auxtrace)
+ rec->buildid_all = true;
+
if (record_opts__config(&rec->opts)) {
err = -EINVAL;
goto out_symbol_exit;
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