perf stat: Improve readability of shadow stats

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

v2:
o do not change 'sec' to 'cpu-sec'.
o use convert_unit_double to implement convert_unit.

Signed-off-by: Changbin Du <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/stat-shadow.c

···
 #include "expr.h"
 #include "metricgroup.h"
 #include "cgroup.h"
+#include "units.h"
 #include <linux/zalloc.h>
 
 /*
···
 		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);

tools/perf/util/units.c

···
 	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)

tools/perf/util/units.h

···
 
 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);