linux-kernel - Re: [PATCH 2/9] perf report: Remove the first overflow check for branch counters

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Message-ID: <CAM9d7chyCh3pEnrFFdBv2xFZqJm9uaaw+PtuFMs0DaOB1T6kjQ@mail.gmail.com>
Date: Fri, 2 Aug 2024 13:26:01 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: kan.liang@...ux.intel.com
Cc: acme@...nel.org, irogers@...gle.com, peterz@...radead.org, 
	mingo@...nel.org, linux-kernel@...r.kernel.org, adrian.hunter@...el.com, 
	ak@...ux.intel.com, eranian@...gle.com
Subject: Re: [PATCH 2/9] perf report: Remove the first overflow check for
 branch counters

On Wed, Jul 3, 2024 at 1:03 PM <kan.liang@...ux.intel.com> wrote:
>
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> A false overflow warning is triggered if a sample doesn't have any LBRs
> recorded and the branch counters feature is enabled.
>
> The current code does OVERFLOW_CHECK_u64() at the very beginning when
> reading the information of branch counters. It assumes that there is at
> least one LBR in the PEBS record. But it is a valid case that 0 LBR is
> recorded especially in a high context switch.
>
> Remove the OVERFLOW_CHECK_u64(). The later OVERFLOW_CHECK() should be
> good enough to check the overflow when reading the information of the
> branch counters.
>
> Fixes: 9fbb4b02302b ("perf tools: Add branch counter knob")
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> ---
>  tools/perf/util/evsel.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index bc603193c477..a5dd031c9080 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2810,8 +2810,6 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
>                 array = (void *)array + sz;
>
>                 if (evsel__has_branch_counters(evsel)) {
> -                       OVERFLOW_CHECK_u64(array);
> -
>                         data->branch_stack_cntr = (u64 *)array;
>                         sz = data->branch_stack->nr * sizeof(u64);
>
> --
> 2.38.1
>