linux-kernel - Re: [PATCH 2/4] perf hist: Simplify hist printing logic for group events

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Date: Wed, 14 Feb 2024 15:57:24 -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>, 
	Adrian Hunter <adrian.hunter@...el.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/4] perf hist: Simplify hist printing logic for group events

On Mon, Feb 12, 2024 at 11:53 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> It can uses an array to save the period (or percent) values for member
> events and print them together in a loop.  This simplify the logic to
> handle missing samples in members with zero values.
>
> No functional change intended.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/ui/hist.c | 55 +++++++++++++++++---------------------------
>  1 file changed, 21 insertions(+), 34 deletions(-)
>
> diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
> index 2bf959d08354..5f4c110d840f 100644
> --- a/tools/perf/ui/hist.c
> +++ b/tools/perf/ui/hist.c
> @@ -33,6 +33,7 @@ static int __hpp__fmt(struct perf_hpp *hpp, struct hist_entry *he,
>         char *buf = hpp->buf;
>         size_t size = hpp->size;
>
> +       /* print stand-alone or group leader events separately */
>         if (fmt_percent) {
>                 double percent = 0.0;
>                 u64 total = hists__total_period(hists);
> @@ -45,12 +46,19 @@ static int __hpp__fmt(struct perf_hpp *hpp, struct hist_entry *he,
>                 ret = hpp__call_print_fn(hpp, print_fn, fmt, len, get_field(he));
>
>         if (evsel__is_group_event(evsel)) {
> -               int prev_idx, idx_delta;
> +               int idx;
>                 struct hist_entry *pair;
>                 int nr_members = evsel->core.nr_members;
> +               union {
> +                       u64 period;
> +                       double percent;
> +               } *val;
>
> -               prev_idx = evsel__group_idx(evsel);
> +               val = calloc(nr_members, sizeof(*val));
> +               if (val == NULL)
> +                       return 0;

Looks good, but should this return value be negative to indicate an
error? Snprintf gives a negative result on error, its result is
sometimes returned from hpp__fmt_acc, as is this result.

Thanks,
Ian

>
> +               /* collect values in the group members */
>                 list_for_each_entry(pair, &he->pairs.head, pairs.node) {
>                         u64 period = get_field(pair);
>                         u64 total = hists__total_period(pair->hists);
> @@ -59,47 +67,26 @@ static int __hpp__fmt(struct perf_hpp *hpp, struct hist_entry *he,
>                                 continue;
>
>                         evsel = hists_to_evsel(pair->hists);
> -                       idx_delta = evsel__group_idx(evsel) - prev_idx - 1;
> -
> -                       while (idx_delta--) {
> -                               /*
> -                                * zero-fill group members in the middle which
> -                                * have no sample
> -                                */
> -                               if (fmt_percent) {
> -                                       ret += hpp__call_print_fn(hpp, print_fn,
> -                                                                 fmt, len, 0.0);
> -                               } else {
> -                                       ret += hpp__call_print_fn(hpp, print_fn,
> -                                                                 fmt, len, 0ULL);
> -                               }
> -                       }
> -
> -                       if (fmt_percent) {
> -                               ret += hpp__call_print_fn(hpp, print_fn, fmt, len,
> -                                                         100.0 * period / total);
> -                       } else {
> -                               ret += hpp__call_print_fn(hpp, print_fn, fmt,
> -                                                         len, period);
> -                       }
> +                       idx = evsel__group_idx(evsel);
>
> -                       prev_idx = evsel__group_idx(evsel);
> +                       if (fmt_percent)
> +                               val[idx].percent = 100.0 * period / total;
> +                       else
> +                               val[idx].period = period;
>                 }
>
> -               idx_delta = nr_members - prev_idx - 1;
> -
> -               while (idx_delta--) {
> -                       /*
> -                        * zero-fill group members at last which have no sample
> -                        */
> +               /* idx starts from 1 to skip the leader event */
> +               for (idx = 1; idx < nr_members; idx++) {
>                         if (fmt_percent) {
>                                 ret += hpp__call_print_fn(hpp, print_fn,
> -                                                         fmt, len, 0.0);
> +                                                         fmt, len, val[idx].percent);
>                         } else {
>                                 ret += hpp__call_print_fn(hpp, print_fn,
> -                                                         fmt, len, 0ULL);
> +                                                         fmt, len, val[idx].period);
>                         }
>                 }
> +
> +               free(val);
>         }
>
>         /*
> --
> 2.43.0.687.g38aa6559b0-goog
>