linux-kernel - Re: [RFC] perf record: missing buildid for callstack modules

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Date:	Sat, 9 Jan 2016 19:31:43 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [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@...nel.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@...gle.com> wrote:
> >> >On Thu, Jan 7, 2016 at 1:59 PM, Arnaldo Carvalho de Melo
> >> ><acme@...nel.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;