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

[Namhyung Kim <namhyung@kernel.org>]

Hi Adrian,

On Mon, Jan 11, 2016 at 11:27:56AM +0200, Adrian Hunter wrote:
> On 09/01/16 12:31, Namhyung Kim wrote:
> > 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?
> 
> If you don't post-process (i.e. call process_buildids), then where do the
> DSOs come from? i.e. dsos__hit_all() just hits the DSOs that exist.

Ah, right.  I somehow thought that it was processed already elsewhere.

Then, how about this?



>From 38b2bc273329afe4334a11d87d20ef71639132fb Mon Sep 17 00:00:00 2001
From: Namhyung Kim <namhyung@kernel.org>
Date: Sat, 9 Jan 2016 22:37:55 +0900
Subject: [PATCH] perf record: Add --buildid-all option

The --buildid-all option is to record build-id of all DSOs in the file.
It might be very costly to postprocess samples to find which DSO hits.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/Documentation/perf-record.txt |  3 +++
 tools/perf/builtin-record.c              | 26 ++++++++++++++++++++------
 2 files changed, 23 insertions(+), 6 deletions(-)

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..319712a4e02b 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;
 };
 
@@ -362,6 +363,13 @@ static int process_buildids(struct record *rec)
 	 */
 	symbol_conf.ignore_vmlinux_buildid = true;
 
+	/*
+	 * If --buildid-all is given, it marks all DSO regardless of hits,
+	 * so no need to process samples.
+	 */
+	if (rec->buildid_all)
+		rec->tool.sample = NULL;
+
 	return perf_session__process_events(session);
 }
 
@@ -756,12 +764,8 @@ out_child:
 
 		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);
 		}
 		perf_session__write_header(rec->session, rec->evlist, fd, true);
@@ -1138,6 +1142,8 @@ 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 +1261,14 @@ 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;
-- 
2.6.4