linux-kernel - [PATCH 2/2] perf tool: don't print bogus data on -e cycles

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Message-Id: <1380539585-23859-3-git-send-email-artagnon@gmail.com>
Date:	Mon, 30 Sep 2013 16:43:05 +0530
From:	Ramkumar Ramachandra <artagnon@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>
Subject: [PATCH 2/2] perf tool: don't print bogus data on -e cycles

When only the cycles event is requested:

$ perf stat -e cycles dd if=/dev/zero of=/dev/null count=1000000
1000000+0 records in
1000000+0 records out
512000000 bytes (512 MB) copied, 0.26123 s, 2.0 GB/s

 Performance counter stats for 'dd if=/dev/zero of=/dev/null count=1000000':

       911,626,453 cycles                    #    0.000 GHz

       0.262113350 seconds time elapsed

The 0.000 GHz comment in the output is totally bogus and misleading. It
happens because update_shadow_stats() doesn't touch runtime_nsecs_stats;
it is only written when a requested counter matches a SW_TASK_CLOCK. In
our case, since we have only requested HW_CPU_CYCLES,
runtime_nsecs_stats is unavailable. So, omit printing the comment
altogether.

Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Signed-off-by: Ramkumar Ramachandra <artagnon@...il.com>
---
 tools/perf/builtin-stat.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index f686d5f..cc167ae 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -918,11 +918,10 @@ static void abs_printout(int cpu, int nr, struct perf_evsel *evsel, double avg)
 		print_stalled_cycles_backend(cpu, evsel, avg);
 	} else if (perf_evsel__match(evsel, HARDWARE, HW_CPU_CYCLES)) {
 		total = avg_stats(&runtime_nsecs_stats[cpu]);
-
-		if (total)
-			ratio = 1.0 * avg / total;
-
-		fprintf(output, " # %8.3f GHz                    ", ratio);
+		if (total) {
+			ratio = avg / total;
+			fprintf(output, " # %8.3f GHz                    ", ratio);
+		}
 	} else if (runtime_nsecs_stats[cpu].n != 0) {
 		char unit = 'M';
 
-- 
1.8.4.477.g5d89aa9

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