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

[James Clark]

On 30/10/2024 2:45 am, Ian Rogers wrote:
> 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.

Yep I'll update it.

> > 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


Here's the stack:

print_metric_json() (stat-display.c:516)
printout() (stat-display.c:912)
print_counter_aggrdata() (stat-display.c:1110)
print_counter() (stat-display.c:1224)
evlist__print_counters() (stat-display.c:1734)
print_counters() (builtin-stat.c:1016)
cmd_stat() (builtin-stat.c:2872)
run_builtin() (perf/perf.c:351)
handle_internal_command() (perf.c:404)
run_argv() (perf.c:448)
main() (perf.c:560)

The empty string is from printout():

  pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL, /*unit=*/"",
     /*val=*/0);

Changing it to NULL seems to work, so is probably a bit neater. I can do 
that if you think that makes sense?

There's another one for --metric-only that I didn't run into, but it 
could also make sense to change:

  if (config->metric_only) {
    pm(config, os, METRIC_THRESHOLD_UNKNOWN, "", "", 0);

> > 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