[PATCH 5/6] perf record: Add switch-output size warning

[Jiri Olsa]

Adding switch-output size warning if the requested
size of lower than the wakeup ring buffer size.

  $ perf record --switch-output=1K ls
  WARNING: switch-output data size lower than wakeup kernel buffer size (258K) expect bigger perf.data sizes
  ...

Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-0gafw11lesghnbfoiw90kc3q@xxxxxxxxxxxxxx
---
 tools/perf/builtin-record.c | 21 +++++++++++++++++++++
 tools/perf/util/evlist.c    |  2 +-
 tools/perf/util/evlist.h    |  2 ++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 3fa64492ee62..4a70e964cd96 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1377,6 +1377,23 @@ static int record__parse_mmap_pages(const struct option *opt,
 	return ret;
 }
 
+static void switch_output_size_warn(struct record *rec)
+{
+	u64 wakeup_size = perf_evlist__mmap_size(rec->opts.mmap_pages);
+	struct switch_output *s = &rec->switch_output;
+
+	wakeup_size /= 2;
+
+	if (s->size < wakeup_size) {
+		char buf[100];
+
+		unit_number__scnprint(buf, sizeof(buf), wakeup_size);
+		pr_warning("WARNING: switch-output data size lower than "
+			   "wakeup kernel buffer size (%s) "
+			   "expect bigger perf.data sizes\n", buf);
+	}
+}
+
 static int switch_output_setup(struct record *rec)
 {
 	struct switch_output *s = &rec->switch_output;
@@ -1410,6 +1427,10 @@ static int switch_output_setup(struct record *rec)
 enabled:
 	rec->timestamp_filename = true;
 	s->enabled              = true;
+
+	if (s->size && !rec->opts.no_buffering)
+		switch_output_size_warn(rec);
+
 	return 0;
 }
 
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 435ff1c94a66..9900ce5177bc 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1184,7 +1184,7 @@ unsigned long perf_event_mlock_kb_in_pages(void)
 	return pages;
 }
 
-static size_t perf_evlist__mmap_size(unsigned long pages)
+size_t perf_evlist__mmap_size(unsigned long pages)
 {
 	if (pages == UINT_MAX)
 		pages = perf_event_mlock_kb_in_pages();
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 4fd034f22d2f..389b9ccdf8c7 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -218,6 +218,8 @@ int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
 		      bool overwrite);
 void perf_evlist__munmap(struct perf_evlist *evlist);
 
+size_t perf_evlist__mmap_size(unsigned long pages);
+
 void perf_evlist__disable(struct perf_evlist *evlist);
 void perf_evlist__enable(struct perf_evlist *evlist);
 void perf_evlist__toggle_enable(struct perf_evlist *evlist);
-- 
2.7.4