Re: [PATCH 2/2] perf stat: Also hide metric from JSON if units are an empty string

[Ian Rogers]

On Tue, Oct 29, 2024 at 5:42 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hello,
>
> On Fri, Oct 25, 2024 at 10:03:05AM +0100, James Clark wrote:
> > We decided to hide NULL metric units rather than showing it as "(null)",
> > but on hybrid systems if the process doesn't hit a PMU you get an empty
> > string metric unit instead. To make it consistent also remove empty
> > strings.
> >
> > Note that metric-threshold is already hidden in this case without this
> > change.
> >
> > Where a process only runs on cpu_core and never hits cpu_atom:
> > Before:
> >  $ perf stat -j -- true
> >  ...
> >  {"counter-value" : "<not counted>", "unit" : "", "event" : "cpu_atom/branch-misses/", "event-runtime" : 0, "pcnt-running" : 0.00, "metric-value" : "0.000000", "metric-unit" : ""}
> >  {"counter-value" : "6326.000000", "unit" : "", "event" : "cpu_core/branch-misses/", "event-runtime" : 293786, "pcnt-running" : 100.00, "metric-value" : "3.553394", "metric-unit" : "of all branches", "metric-threshold" : "good"}
> >  ...
>
> I guess you're talking about "metric-unit", not plain "unit", right?
> Then please update the subject line to reduce the config.
>
> Ian, can you please review?

It'd be nice to see the stack trace for when metric-unit is "" as I'm
not seeing the logic in stat-shadow.c. If we know the caller than it
seems logical the unit can be passed as NULL rather than "".

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > After:
> >  ...
> >  {"counter-value" : "<not counted>", "unit" : "", "event" : "cpu_atom/branch-misses/", "event-runtime" : 0, "pcnt-running" : 0.00}
> >  {"counter-value" : "5778.000000", "unit" : "", "event" : "cpu_core/branch-misses/", "event-runtime" : 282240, "pcnt-running" : 100.00, "metric-value" : "3.226797", "metric-unit" : "of all branches", "metric-threshold" : "good"}
> >  ...
> >
> > Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> > ---
> >  tools/perf/util/stat-display.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> > index a5d72f4a515c..9b7fd985a42a 100644
> > --- a/tools/perf/util/stat-display.c
> > +++ b/tools/perf/util/stat-display.c
> > @@ -506,7 +506,7 @@ static void print_metric_json(struct perf_stat_config *config __maybe_unused,
> >       struct outstate *os = ctx;
> >       FILE *out = os->fh;
> >
> > -     if (unit) {
> > +     if (unit && strlen(unit)) {
> >               json_out(os, "\"metric-value\" : \"%f\", \"metric-unit\" : \"%s\"", val, unit);
> >               if (thresh != METRIC_THRESHOLD_UNKNOWN) {
> >                       json_out(os, "\"metric-threshold\" : \"%s\"",
> > --
> > 2.34.1
> >