[PATCH v7 2/6] perf record: Get the first sample time and last sample time

[Jin Yao]

In the default 'perf record' configuration, all samples are processed,
to create the HEADER_BUILD_ID table. So it's very easy to get the
first/last samples and save the time to perf file header via the
function write_sample_time().

Later, at post processing time, perf report/script will fetch
the time from perf file header.

Change log:
-----------
v7: Just update the patch description according to Arnaldo's suggestion.

v6: Currently '--buildid-all' is not enabled at default. So the walking
    on all samples is the default operation. There is no big overhead
    to calculate the timestamp boundary in process_sample_event handler
    once we already go through all samples. So the timestamp boundary
    calculation is enabled by default when '--buildid-all' is not enabled.

    While if '--buildid-all' is enabled, we creates a new option
    "--timestamp-boundary" for user to decide if it enables the
    timestamp boundary calculation.

v5: There is an issue that the sample walking can only work when
    '--buildid-all' is not enabled. So we need to let the walking
    be able to work even if '--buildid-all' is enabled and let the
    processing skips the dso hit marking for this case.

    At first, I want to provide a new option "--record-time-boundaries".
    While after consideration, I think a new option is not very
    necessary.

v3: Remove the definitions of first_sample_time and last_sample_time
    from struct record and directly save them in perf_evlist.

Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
 tools/perf/Documentation/perf-record.txt |  3 +++
 tools/perf/builtin-record.c              | 18 +++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 5a626ef..3eea6de 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -430,6 +430,9 @@ Configure all used events to run in user space.
 --timestamp-filename
 Append timestamp to output file name.
 
+--timestamp-boundary::
+Record timestamp boundary (time of first/last samples).
+
 --switch-output[=mode]::
 Generate multiple perf.data files, timestamp prefixed, switching to a new one
 based on 'mode' value:
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 98da8cb..6db7b5a 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -78,6 +78,7 @@ struct record {
 	bool			no_buildid_cache_set;
 	bool			buildid_all;
 	bool			timestamp_filename;
+	bool			timestamp_boundary;
 	struct switch_output	switch_output;
 	unsigned long long	samples;
 };
@@ -409,8 +410,15 @@ static int process_sample_event(struct perf_tool *tool,
 {
 	struct record *rec = container_of(tool, struct record, tool);
 
-	rec->samples++;
+	if (rec->evlist->first_sample_time == 0)
+		rec->evlist->first_sample_time = sample->time;
+
+	rec->evlist->last_sample_time = sample->time;
 
+	if (rec->buildid_all)
+		return 0;
+
+	rec->samples++;
 	return build_id__mark_dso_hit(tool, event, sample, evsel, machine);
 }
 
@@ -435,9 +443,11 @@ static int process_buildids(struct record *rec)
 
 	/*
 	 * If --buildid-all is given, it marks all DSO regardless of hits,
-	 * so no need to process samples.
+	 * so no need to process samples. But if timestamp_boundary is enabled,
+	 * it still needs to walk on all samples to get the timestamps of
+	 * first/last samples.
 	 */
-	if (rec->buildid_all)
+	if (rec->buildid_all && !rec->timestamp_boundary)
 		rec->tool.sample = NULL;
 
 	return perf_session__process_events(session);
@@ -1621,6 +1631,8 @@ static struct option __record_options[] = {
 		    "Record build-id of all DSOs regardless of hits"),
 	OPT_BOOLEAN(0, "timestamp-filename", &record.timestamp_filename,
 		    "append timestamp to output filename"),
+	OPT_BOOLEAN(0, "timestamp-boundary", &record.timestamp_boundary,
+		    "Record timestamp boundary (time of first/last samples)"),
 	OPT_STRING_OPTARG_SET(0, "switch-output", &record.switch_output.str,
 			  &record.switch_output.set, "signal,size,time",
 			  "Switch output when receive SIGUSR2 or cross size,time threshold",
-- 
2.7.4