[tip:perfcounters/urgent] perf stat: Add -n/--null option to run without counters

[tip-bot for Ingo Molnar]

Commit-ID:  0cfb7a13b8e4e0afd4b856156ab16a182de7505b
Gitweb:     http://git.kernel.org/tip/0cfb7a13b8e4e0afd4b856156ab16a182de7505b
Author:     Ingo Molnar <mingo@xxxxxxx>
AuthorDate: Sat, 27 Jun 2009 06:10:30 +0200
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sat, 27 Jun 2009 06:11:24 +0200

perf stat: Add -n/--null option to run without counters

Allow a no-counters run. This can be useful to measure just
elapsed wall-clock time - or to assess the raw overhead of perf
stat itself, without running any counters.

Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>


---
 tools/perf/builtin-stat.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 8420ec5..cdcd058 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -70,6 +70,7 @@ static int			run_count			=  1;
 static int			inherit				=  1;
 static int			scale				=  1;
 static int			target_pid			= -1;
+static int			null_run			=  0;
 
 static int			fd[MAX_NR_CPUS][MAX_COUNTERS];
 
@@ -461,6 +462,8 @@ static const struct option options[] = {
 		    "be more verbose (show counter open errors, etc)"),
 	OPT_INTEGER('r', "repeat", &run_count,
 		    "repeat command and print average + stddev (max: 100)"),
+	OPT_BOOLEAN('n', "null", &null_run,
+		    "null run - dont start any counters"),
 	OPT_END()
 };
 
@@ -476,7 +479,7 @@ int cmd_stat(int argc, const char **argv, const char *prefix)
 	if (run_count <= 0 || run_count > MAX_RUN)
 		usage_with_options(stat_usage, options);
 
-	if (!nr_counters)
+	if (!null_run && !nr_counters)
 		nr_counters = 8;
 
 	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
--
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