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

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Message-ID: <06c73597-5b23-4759-9101-6594cc13cabc@linux.intel.com>
Date: Wed, 6 Nov 2024 11:23:15 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...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



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

> 
> While we're talking metrics, I'm still looking for feedback on the
> python generation of metrics. v1 was sent back in January, if v4 looks
> okay some acknowledgement would be nice:
> https://lore.kernel.org/lkml/CAP-5=fVX5wypmAAhR8LsE4nSWp5BmN_qhGf9+WCh2bebNcGYTg@mail.gmail.com/
> Leo sent some feedback to improve some of the ARM metrics, so I can
> resend the whole series. Would be nice to gather some acked-by or
> other tags.
> 

Somehow I missed your last reply. I will take a look.

Thanks,
Kan