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

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Message-ID: <a6f60420-e6fc-4b9d-8487-7ca8d3dc56e9@linux.intel.com>
Date: Thu, 7 Nov 2024 14:38:21 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Namhyung Kim <namhyung@...nel.org>
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



On 2024-11-07 2:07 p.m., Namhyung Kim wrote:
> 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?
> 

Yes.

Acked-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan
> Thanks,
> Namhyung
>