linux-kernel - Re: [PATCH v1] perf stat: Expand metric+unit buffer size

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Message-ID: <Zy0P1POgAe_fkLBF@google.com>
Date: Thu, 7 Nov 2024 11:07:00 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Ian Rogers <irogers@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf stat: Expand metric+unit buffer size

Hi Kan,

On Wed, Nov 06, 2024 at 11:23:15AM -0500, Liang, Kan wrote:
> 
> 
> On 2024-11-06 11:04 a.m., Ian Rogers wrote:
> > On Wed, Nov 6, 2024 at 7:27 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
> >>
> >>
> >>
> >> On 2024-11-05 7:48 p.m., Ian Rogers wrote:
> >>> Long metric names combined with units may exceed the metric_bf and
> >>> lead to truncation. Double metric_bf in size to avoid this.
> >>>
> >>> Signed-off-by: Ian Rogers <irogers@...gle.com>
> >>> ---
> >>>  tools/perf/util/stat-shadow.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
> >>> index 8c9292aa61d3..6b531d4f58a3 100644
> >>> --- a/tools/perf/util/stat-shadow.c
> >>> +++ b/tools/perf/util/stat-shadow.c
> >>> @@ -507,7 +507,7 @@ static void generic_metric(struct perf_stat_config *config,
> >>>       if (!metric_events[i]) {
> >>>               if (expr__parse(&ratio, pctx, metric_expr) == 0) {
> >>>                       char *unit;
> >>> -                     char metric_bf[64];
> >>> +                     char metric_bf[128];
> >>
> >> I thin there is already a MAX_EVENT_NAME.
> >> Can we similarly define a MAX_METRIC_NAME for it?
> > 
> > So in this case the buffer needs to be big enough to hold the metric
> > name, the unit from the scaleunit (e.g. the "%" from "100%"). I'd
> > prefer we used dynamic memory allocation to having hard coded limits,
> > just to avoid a "640K ought to be enough for anybody," moment.
> > Although this change is implicitly a hard coded limit, sigh. There is
> > also the metric only name length:
> > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/builtin-stat.c?h=perf-tools-next#n160
> > That looked like it was planned to be dynamically computed but then
> > the patch adding that never materialized - meaning "standard"
> > metric-only output has its own cut-off rules at 20 characters. I'd
> > rather wait on doing a larger cleanup and do this quick fix for now,
> > mainly as I have enough to do.
> 
> OK

Can I assume it as Acked-by?

Thanks,
Namhyung