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

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Message-ID: <1ab9d5be-b31b-4f76-9ccd-001603a55e53@linaro.org>
Date: Wed, 30 Oct 2024 09:36:37 +0000
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>, Namhyung Kim <namhyung@...nel.org>
Cc: linux-perf-users@...r.kernel.org, acme@...nel.org,
 tim.c.chen@...ux.intel.com, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>,
 Yicong Yang <yangyicong@...ilicon.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf stat: Also hide metric from JSON if units are an
 empty string



On 30/10/2024 2:45 am, Ian Rogers wrote:
> On Tue, Oct 29, 2024 at 5:42 PM Namhyung Kim <namhyung@...nel.org> 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@...aro.org>
>>> ---
>>>   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
>>>