perf record: Add switch-output size warning

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@kernel.org>
Suggested-and-Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1483955520-29063-6-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 3fa64492ee62..93319e1be3ac 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1377,6 +1377,23 @@ out_free:
 	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__scnprintf(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;
 }