[tip:perfcounters/core] perf stat: Change noise calculation to use stddev

tip-bot for Peter Zijlstra
2009-09-04T15:43:32Z

Commit-ID: 506d4bc8d5dab20d84624aa07cdc6dcd77915d52
Gitweb: http://git.kernel.org/tip/506d4bc8d5dab20d84624aa07cdc6dcd77915d52
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 4 Sep 2009 15:36:12 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 4 Sep 2009 16:33:07 +0200

perf stat: Change noise calculation to use stddev

The current noise computation does:

\Sum abs(n_i - avg(n)) * N^-1.5

Which is (afaik) not a regular noise function, and needs the
complete sample set available to post-process.

Change this to use a regular stddev computation which can be
done by keeping a two sums:

stddev = sqrt( 1/N (\Sum n_i^2) - avg(n)^2 )

For which we only need to keep \Sum n_i and \Sum n_i^2.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
tools/perf/builtin-stat.c | 170 ++++++++++++++++++---------------------------
1 files changed, 69 insertions(+), 101 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 1a26262..31ffc4d 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -83,19 +83,32 @@ static u64 runtime_cycles[MAX_RUN];
static u64 event_res[MAX_RUN][MAX_COUNTERS][3];
static u64 event_scaled[MAX_RUN][MAX_COUNTERS];

-static u64 event_res_avg[MAX_COUNTERS][3];
-static u64 event_res_noise[MAX_COUNTERS][3];
+struct stats
+{
+ double sum;
+ double sum_sq;
+};

-static u64 event_scaled_avg[MAX_COUNTERS];
+static double avg_stats(struct stats *stats)
+{
+ return stats->sum / run_count;
+}

-static u64 runtime_nsecs_avg;
-static u64 runtime_nsecs_noise;
+/*
+ * stddev = sqrt(1/N (\Sum n_i^2) - avg(n)^2)
+ */
+static double stddev_stats(struct stats *stats)
+{
+ double avg = stats->sum / run_count;

-static u64 walltime_nsecs_avg;
-static u64 walltime_nsecs_noise;
+ return sqrt(stats->sum_sq/run_count - avg*avg);
+}

-static u64 runtime_cycles_avg;
-static u64 runtime_cycles_noise;
+struct stats event_res_stats[MAX_COUNTERS][3];
+struct stats event_scaled_stats[MAX_COUNTERS];
+struct stats runtime_nsecs_stats;
+struct stats walltime_nsecs_stats;
+struct stats runtime_cycles_stats;

#define MATCH_EVENT(t, c, counter) \
(attrs[counter].type == PERF_TYPE_##t && \
@@ -279,42 +292,37 @@ static int run_perf_stat(int argc __used, const char **argv)
return WEXITSTATUS(status);
}

-static void print_noise(u64 *count, u64 *noise)
+static void print_noise(double avg, double stddev)
{
if (run_count > 1)
- fprintf(stderr, " ( +- %7.3f%% )",
- (double)noise[0]/(count[0]+1)*100.0);
+ fprintf(stderr, " ( +- %7.3f%% )", 100*stddev / avg);
}

-static void nsec_printout(int counter, u64 *count, u64 *noise)
+static void nsec_printout(int counter, double avg, double stddev)
{
- double msecs = (double)count[0] / 1000000;
+ double msecs = avg / 1e6;

fprintf(stderr, " %14.6f %-24s", msecs, event_name(counter));

if (MATCH_EVENT(SOFTWARE, SW_TASK_CLOCK, counter)) {
- if (walltime_nsecs_avg)
- fprintf(stderr, " # %10.3f CPUs ",
- (double)count[0] / (double)walltime_nsecs_avg);
+ fprintf(stderr, " # %10.3f CPUs ",
+ avg / avg_stats(&walltime_nsecs_stats));
}
- print_noise(count, noise);
+ print_noise(avg, stddev);
}

-static void abs_printout(int counter, u64 *count, u64 *noise)
+static void abs_printout(int counter, double avg, double stddev)
{
- fprintf(stderr, " %14Ld %-24s", count[0], event_name(counter));
+ fprintf(stderr, " %14.0f %-24s", avg, event_name(counter));

- if (runtime_cycles_avg &&
- MATCH_EVENT(HARDWARE, HW_INSTRUCTIONS, counter)) {
+ if (MATCH_EVENT(HARDWARE, HW_INSTRUCTIONS, counter)) {
fprintf(stderr, " # %10.3f IPC ",
- (double)count[0] / (double)runtime_cycles_avg);
+ avg / avg_stats(&runtime_cycles_stats));
} else {
- if (runtime_nsecs_avg) {
- fprintf(stderr, " # %10.3f M/sec",
- (double)count[0]/runtime_nsecs_avg*1000.0);
- }
+ fprintf(stderr, " # %10.3f M/sec",
+ 1000.0 * avg / avg_stats(&runtime_nsecs_stats));
}
- print_noise(count, noise);
+ print_noise(avg, stddev);
}

/*
@@ -322,12 +330,12 @@ static void abs_printout(int counter, u64 *count, u64 *noise)
*/
static void print_counter(int counter)
{
- u64 *count, *noise;
+ double avg, stddev;
int scaled;

- count = event_res_avg[counter];
- noise = event_res_noise[counter];
- scaled = event_scaled_avg[counter];
+ avg = avg_stats(&event_res_stats[counter][0]);
+ stddev = stddev_stats(&event_res_stats[counter][0]);
+ scaled = avg_stats(&event_scaled_stats[counter]);

if (scaled == -1) {
fprintf(stderr, " %14s %-24s\n",
@@ -336,36 +344,34 @@ static void print_counter(int counter)
}

if (nsec_counter(counter))
- nsec_printout(counter, count, noise);
+ nsec_printout(counter, avg, stddev);
else
- abs_printout(counter, count, noise);
+ abs_printout(counter, avg, stddev);
+
+ if (scaled) {
+ double avg_enabled, avg_running;
+
+ avg_enabled = avg_stats(&event_res_stats[counter][1]);
+ avg_running = avg_stats(&event_res_stats[counter][2]);

- if (scaled)
fprintf(stderr, " (scaled from %.2f%%)",
- (double) count[2] / count[1] * 100);
+ 100 * avg_running / avg_enabled);
+ }

fprintf(stderr, "\n");
}

-/*
- * normalize_noise noise values down to stddev:
- */
-static void normalize_noise(u64 *val)
+static void update_stats(const char *name, int idx, struct stats *stats, u64 *val)
{
- double res;
+ double sq = *val;

- res = (double)*val / (run_count * sqrt((double)run_count));
-
- *val = (u64)res;
-}
-
-static void update_avg(const char *name, int idx, u64 *avg, u64 *val)
-{
- *avg += *val;
+ stats->sum += *val;
+ stats->sum_sq += sq * sq;

if (verbose > 1)
fprintf(stderr, "debug: %20s[%d]: %Ld\n", name, idx, *val);
}
+
/*
* Calculate the averages and noises:
*/
@@ -377,61 +383,22 @@ static void calc_avg(void)
fprintf(stderr, "\n");

for (i = 0; i < run_count; i++) {
- update_avg("runtime", 0, &runtime_nsecs_avg, runtime_nsecs + i);
- update_avg("walltime", 0, &walltime_nsecs_avg, walltime_nsecs + i);
- update_avg("runtime_cycles", 0, &runtime_cycles_avg, runtime_cycles + i);
+ update_stats("runtime", 0, &runtime_nsecs_stats, runtime_nsecs + i);
+ update_stats("walltime", 0, &walltime_nsecs_stats, walltime_nsecs + i);
+ update_stats("runtime_cycles", 0, &runtime_cycles_stats, runtime_cycles + i);

for (j = 0; j < nr_counters; j++) {
- update_avg("counter/0", j,
- event_res_avg[j]+0, event_res[i][j]+0);
- update_avg("counter/1", j,
- event_res_avg[j]+1, event_res[i][j]+1);
- update_avg("counter/2", j,
- event_res_avg[j]+2, event_res[i][j]+2);
+ update_stats("counter/0", j,
+ event_res_stats[j]+0, event_res[i][j]+0);
+ update_stats("counter/1", j,
+ event_res_stats[j]+1, event_res[i][j]+1);
+ update_stats("counter/2", j,
+ event_res_stats[j]+2, event_res[i][j]+2);
if (event_scaled[i][j] != (u64)-1)
- update_avg("scaled", j,
- event_scaled_avg + j, event_scaled[i]+j);
- else
- event_scaled_avg[j] = -1;
+ update_stats("scaled", j,
+ event_scaled_stats + j, event_scaled[i]+j);
}
}
- runtime_nsecs_avg /= run_count;
- walltime_nsecs_avg /= run_count;
- runtime_cycles_avg /= run_count;
-
- for (j = 0; j < nr_counters; j++) {
- event_res_avg[j][0] /= run_count;
- event_res_avg[j][1] /= run_count;
- event_res_avg[j][2] /= run_count;
- }
-
- for (i = 0; i < run_count; i++) {
- runtime_nsecs_noise +=
- abs((s64)(runtime_nsecs[i] - runtime_nsecs_avg));
- walltime_nsecs_noise +=
- abs((s64)(walltime_nsecs[i] - walltime_nsecs_avg));
- runtime_cycles_noise +=
- abs((s64)(runtime_cycles[i] - runtime_cycles_avg));
-
- for (j = 0; j < nr_counters; j++) {
- event_res_noise[j][0] +=
- abs((s64)(event_res[i][j][0] - event_res_avg[j][0]));
- event_res_noise[j][1] +=
- abs((s64)(event_res[i][j][1] - event_res_avg[j][1]));
- event_res_noise[j][2] +=
- abs((s64)(event_res[i][j][2] - event_res_avg[j][2]));
- }
- }
-
- normalize_noise(&runtime_nsecs_noise);
- normalize_noise(&walltime_nsecs_noise);
- normalize_noise(&runtime_cycles_noise);
-
- for (j = 0; j < nr_counters; j++) {
- normalize_noise(&event_res_noise[j][0]);
- normalize_noise(&event_res_noise[j][1]);
- normalize_noise(&event_res_noise[j][2]);
- }
}

static void print_stat(int argc, const char **argv)
@@ -458,10 +425,11 @@ static void print_stat(int argc, const char **argv)

fprintf(stderr, "\n");
fprintf(stderr, " %14.9f seconds time elapsed",
- (double)walltime_nsecs_avg/1e9);
+ avg_stats(&walltime_nsecs_stats)/1e9);
if (run_count > 1) {
fprintf(stderr, " ( +- %7.3f%% )",
- 100.0*(double)walltime_nsecs_noise/(double)walltime_nsecs_avg);
+ 100*stddev_stats(&walltime_nsecs_stats) /
+ avg_stats(&walltime_nsecs_stats));
}
fprintf(stderr, "\n\n");
}