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

Jiri Olsa
2021-03-02T03:08:12Z

On Tue, Mar 02, 2021 at 01:24:02AM +0800, Changbin Du wrote:
> This does follow two changes:
> 1) Select appropriate unit between K/M/G.
> 2) Use 'cpu-sec' instead of 'sec' to state this is not the wall-time.
>
> $ 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':
>
> 8,003.20 msec cpu-clock # 3.998 CPUs utilized
> 9,768 context-switches # 1.221 K/cpu-sec
> 164 cpu-migrations # 20.492 /cpu-sec

should you remove also the leading '/' in ' /cpu-sec' ?

SNIP

> @@ -1270,18 +1271,14 @@ 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 = ' ';
> char unit_buf[10];
>
> 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);
> +
> + snprintf(unit_buf, sizeof(unit_buf), "%c/cpu-sec", unit);
> print_metric(config, ctxp, NULL, "%8.3f", unit_buf, ratio);

hum this will change -x output that people parse, so I don't think we can do that

> } 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..ac13b5ecde31 100644
> --- a/tools/perf/util/units.c
> +++ b/tools/perf/util/units.c
> @@ -55,6 +55,28 @@ unsigned long convert_unit(unsigned long value, char *unit)
> return value;
> }
>
> +double convert_unit_double(double value, char *unit)
> +{
> + *unit = ' ';
> +
> + if (value > 1000.0) {
> + value /= 1000.0;
> + *unit = 'K';
> + }
> +
> + if (value > 1000.0) {
> + value /= 1000.0;
> + *unit = 'M';
> + }
> +
> + if (value > 1000.0) {
> + value /= 1000.0;
> + *unit = 'G';
> + }
> +
> + return value;
> +}

we have convert_unit function just above doing the same only with
unsigned long.. let's have one base function with double values and
another one casting the result to unsigned long

jirka