[PATCH v2] perf stat: improve readability of shadow stats

[Changbin Du]

This adds function convert_unit_double() and selects appropriate
unit for shadow stats between K/M/G.

$ sudo ./perf stat -a -- sleep 1

Before: Unit 'M' is selected even the number is very small.
 Performance counter stats for 'system wide':

          4,003.06 msec cpu-clock                 #    3.998 CPUs utilized
            16,179      context-switches          #    0.004 M/sec
               161      cpu-migrations            #    0.040 K/sec
             4,699      page-faults               #    0.001 M/sec
     6,135,801,925      cycles                    #    1.533 GHz                      (83.21%)
     5,783,308,491      stalled-cycles-frontend   #   94.26% frontend cycles idle     (83.21%)
     4,543,694,050      stalled-cycles-backend    #   74.05% backend cycles idle      (66.49%)
     4,720,130,587      instructions              #    0.77  insn per cycle
                                                  #    1.23  stalled cycles per insn  (83.28%)
       753,848,078      branches                  #  188.318 M/sec                    (83.61%)
        37,457,747      branch-misses             #    4.97% of all branches          (83.48%)

       1.001283725 seconds time elapsed

After:
$ sudo ./perf stat -a -- sleep 2

 Performance counter stats for 'system wide':

          8,005.52 msec cpu-clock                 #    3.999 CPUs utilized
            10,715      context-switches          #    1.338 K/sec
               785      cpu-migrations            #   98.057 /sec
               102      page-faults               #   12.741 /sec
     1,948,202,279      cycles                    #    0.243 GHz
     2,816,470,932      stalled-cycles-frontend   #  144.57% frontend cycles idle
     2,661,172,207      stalled-cycles-backend    #  136.60% backend cycles idle
       464,172,105      instructions              #    0.24  insn per cycle
                                                  #    6.07  stalled cycles per insn
        91,567,662      branches                  #   11.438 M/sec
         7,756,054      branch-misses             #    8.47% of all branches

       2.002040043 seconds time elapsed

Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>

v2:
  o do not change 'sec' to 'cpu-sec'.
  o use convert_unit_double to implement convert_unit.
---
 tools/perf/util/stat-shadow.c | 16 +++++++---------
 tools/perf/util/units.c       | 21 ++++++++++++++-------
 tools/perf/util/units.h       |  1 +
 3 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index 6ccf21a72f06..3f800e71126f 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -9,6 +9,7 @@
 #include "expr.h"
 #include "metricgroup.h"
 #include "cgroup.h"
+#include "units.h"
 #include <linux/zalloc.h>
 
 /*
@@ -1270,18 +1271,15 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config,
 		generic_metric(config, evsel->metric_expr, evsel->metric_events, NULL,
 				evsel->name, evsel->metric_name, NULL, 1, cpu, out, st);
 	} else if (runtime_stat_n(st, STAT_NSECS, cpu, &rsd) != 0) {
-		char unit = 'M';
-		char unit_buf[10];
+		char unit = ' ';
+		char unit_buf[10] = "/sec";
 
 		total = runtime_stat_avg(st, STAT_NSECS, cpu, &rsd);
-
 		if (total)
-			ratio = 1000.0 * avg / total;
-		if (ratio < 0.001) {
-			ratio *= 1000;
-			unit = 'K';
-		}
-		snprintf(unit_buf, sizeof(unit_buf), "%c/sec", unit);
+			ratio = convert_unit_double(1000000000.0 * avg / total, &unit);
+
+		if (unit != ' ')
+			snprintf(unit_buf, sizeof(unit_buf), "%c/sec", unit);
 		print_metric(config, ctxp, NULL, "%8.3f", unit_buf, ratio);
 	} else if (perf_stat_evsel__is(evsel, SMI_NUM)) {
 		print_smi_cost(config, cpu, out, st, &rsd);
diff --git a/tools/perf/util/units.c b/tools/perf/util/units.c
index a46762aec4c9..32c39cfe209b 100644
--- a/tools/perf/util/units.c
+++ b/tools/perf/util/units.c
@@ -33,28 +33,35 @@ unsigned long parse_tag_value(const char *str, struct parse_tag *tags)
 	return (unsigned long) -1;
 }
 
-unsigned long convert_unit(unsigned long value, char *unit)
+double convert_unit_double(double value, char *unit)
 {
 	*unit = ' ';
 
-	if (value > 1000) {
-		value /= 1000;
+	if (value > 1000.0) {
+		value /= 1000.0;
 		*unit = 'K';
 	}
 
-	if (value > 1000) {
-		value /= 1000;
+	if (value > 1000.0) {
+		value /= 1000.0;
 		*unit = 'M';
 	}
 
-	if (value > 1000) {
-		value /= 1000;
+	if (value > 1000.0) {
+		value /= 1000.0;
 		*unit = 'G';
 	}
 
 	return value;
 }
 
+unsigned long convert_unit(unsigned long value, char *unit)
+{
+	double v = convert_unit_double((double)value, unit);
+
+	return (unsigned long)v;
+}
+
 int unit_number__scnprintf(char *buf, size_t size, u64 n)
 {
 	char unit[4] = "BKMG";
diff --git a/tools/perf/util/units.h b/tools/perf/util/units.h
index 99263b6a23f7..ea43e74e3240 100644
--- a/tools/perf/util/units.h
+++ b/tools/perf/util/units.h
@@ -12,6 +12,7 @@ struct parse_tag {
 
 unsigned long parse_tag_value(const char *str, struct parse_tag *tags);
 
+double convert_unit_double(double value, char *unit);
 unsigned long convert_unit(unsigned long value, char *unit);
 int unit_number__scnprintf(char *buf, size_t size, u64 n);
 
-- 
2.25.1