linux-kernel - Re: [PATCH 15/15] perf stat: Tidy up JSON metric-only output when no metrics

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Message-ID: <CAP-5=fVaUFDwcP9s8aAtxFtRWQnBqRBrZYkKxAxzog_pmicsRQ@mail.gmail.com>
Date:   Wed, 23 Nov 2022 15:31:26 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        James Clark <james.clark@....com>,
        Athira Jajeev <atrajeev@...ux.vnet.ibm.com>
Subject: Re: [PATCH 15/15] perf stat: Tidy up JSON metric-only output when no metrics

On Wed, Nov 23, 2022 at 10:02 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> It printed empty strings for each metric.  I guess it's needed for CSV
> output to match the column number.  We could just ignore the empty
> metrics in JSON but it ended up with a broken JSON object with a
> trailing comma.
>
> So I added a dummy '"metric-value" : "none"' part.  To do that, it
> needs to pass struct outstate to print_metric_end() to check if any
> metric value is printed or not.
>
> Before:
>   # perf stat -aj --metric-only --per-socket --for-each-cgroup system.slice true
>   {"socket" : "S0", "cpu-count" : 8, "cgroup" : "system.slice", "" : "", "" : "", "" : "", "" : "", "" : "", "" : "", "" : "", "" : ""}
>
> After:
>   # perf stat -aj --metric-only --per-socket --for-each-cgroup system.slice true
>   {"socket" : "S0", "cpu-count" : 8, "cgroup" : "system.slice", "metric-value" : "none"}
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/util/stat-display.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> index 7a39a1a7261d..847acdb5dc40 100644
> --- a/tools/perf/util/stat-display.c
> +++ b/tools/perf/util/stat-display.c
> @@ -532,6 +532,8 @@ static void print_metric_only_json(struct perf_stat_config *config __maybe_unuse
>         while (isdigit(*ends) || *ends == '.')
>                 ends++;
>         *ends = 0;
> +       if (!unit[0] || !vals[0])
> +               return;
>         fprintf(out, "%s\"%s\" : \"%s\"", os->first ? "" : ", ", unit, vals);
>         os->first = false;
>  }
> @@ -864,14 +866,19 @@ static void print_metric_begin(struct perf_stat_config *config,
>         print_cgroup(config, os->cgrp ? : evsel->cgrp);
>  }
>
> -static void print_metric_end(struct perf_stat_config *config)
> +static void print_metric_end(struct perf_stat_config *config, struct outstate *os)
>  {
> +       FILE *output = config->output;
> +
>         if (!config->metric_only)
>                 return;
>
> -       if (config->json_output)
> -               fputc('}', config->output);
> -       fputc('\n', config->output);
> +       if (config->json_output) {
> +               if (os->first)
> +                       fputs("\"metric-value\" : \"none\"", output);
> +               fputc('}', output);
> +       }
> +       fputc('\n', output);
>  }
>
>  static void print_aggr(struct perf_stat_config *config,
> @@ -897,7 +904,7 @@ static void print_aggr(struct perf_stat_config *config,
>
>                         print_counter_aggrdata(config, counter, s, os);
>                 }
> -               print_metric_end(config);
> +               print_metric_end(config, os);
>         }
>  }
>
> @@ -929,7 +936,7 @@ static void print_aggr_cgroup(struct perf_stat_config *config,
>
>                                 print_counter_aggrdata(config, counter, s, os);
>                         }
> -                       print_metric_end(config);
> +                       print_metric_end(config, os);
>                 }
>         }
>  }
> @@ -985,7 +992,7 @@ static void print_no_aggr_metric(struct perf_stat_config *config,
>                         printout(config, os, uval, run, ena, 1.0, counter_idx);
>                 }
>                 if (!first)
> -                       print_metric_end(config);
> +                       print_metric_end(config, os);
>         }
>  }
>
> @@ -1348,7 +1355,7 @@ static void print_cgroup_counter(struct perf_stat_config *config, struct evlist
>         evlist__for_each_entry(evlist, counter) {
>                 if (os->cgrp != counter->cgrp) {
>                         if (os->cgrp != NULL)
> -                               print_metric_end(config);
> +                               print_metric_end(config, os);
>
>                         os->cgrp = counter->cgrp;
>                         print_metric_begin(config, evlist, os, /*aggr_idx=*/0);
> @@ -1357,7 +1364,7 @@ static void print_cgroup_counter(struct perf_stat_config *config, struct evlist
>                 print_counter(config, counter, os);
>         }
>         if (os->cgrp)
> -               print_metric_end(config);
> +               print_metric_end(config, os);
>  }
>
>  void evlist__print_counters(struct evlist *evlist, struct perf_stat_config *config,
> @@ -1405,7 +1412,7 @@ void evlist__print_counters(struct evlist *evlist, struct perf_stat_config *conf
>                         evlist__for_each_entry(evlist, counter) {
>                                 print_counter(config, counter, &os);
>                         }
> -                       print_metric_end(config);
> +                       print_metric_end(config, &os);
>                 }
>                 break;
>         case AGGR_NONE:
> --
> 2.38.1.584.g0f3c55d4c2-goog
>