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

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Date:   Thu, 4 Mar 2021 16:22:09 +0000
From:   Changbin Du <changbin.du@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Changbin Du <changbin.du@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Ian Rogers <irogers@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] perf stat: improve readability of shadow stats

On Mon, Mar 01, 2021 at 08:19:20PM +0100, Jiri Olsa wrote:
> 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
okay, so skip this change and keep another.

-- 
Cheers,
Changbin Du