linux-kernel - Re: [PATCH v5 05/17] perf: cs-etm: Only save valid trace IDs into files

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Message-ID: <CAJ9a7Vh9GwbFZQDH=FedjnvdVPrOQnftCpu2CBh4EFT=kbg_2Q@mail.gmail.com>
Date: Thu, 18 Jul 2024 14:24:34 +0100
From: Mike Leach <mike.leach@...aro.org>
To: James Clark <james.clark@...aro.org>
Cc: coresight@...ts.linaro.org, suzuki.poulose@....com, 
	gankulkarni@...amperecomputing.com, leo.yan@...ux.dev, 
	anshuman.khandual@....com, James Clark <james.clark@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>, 
	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>, Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, "Liang, Kan" <kan.liang@...ux.intel.com>, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-stm32@...md-mailman.stormreply.com, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v5 05/17] perf: cs-etm: Only save valid trace IDs into files

On Fri, 12 Jul 2024 at 11:22, James Clark <james.clark@...aro.org> wrote:
>
> From: James Clark <james.clark@....com>
>
> This isn't a bug because Perf always masks with
> CORESIGHT_TRACE_ID_VAL_MASK before using these values, but to avoid it
> looking like it could be, make an effort to not save bad values.
>
> Signed-off-by: James Clark <james.clark@....com>
> Signed-off-by: James Clark <james.clark@...aro.org>
> ---
>  tools/perf/arch/arm/util/cs-etm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index b0118546cd4d..14b8afabce3a 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -643,7 +643,8 @@ static bool cs_etm_is_ete(struct perf_pmu *cs_etm_pmu, struct perf_cpu cpu)
>
>  static __u64 cs_etm_get_legacy_trace_id(struct perf_cpu cpu)
>  {
> -       return CORESIGHT_LEGACY_CPU_TRACE_ID(cpu.cpu);
> +       /* Wrap at 48 so that invalid trace IDs aren't saved into files. */
> +       return CORESIGHT_LEGACY_CPU_TRACE_ID(cpu.cpu % 48);
>  }
>
>  static void cs_etm_save_etmv4_header(__u64 data[], struct auxtrace_record *itr, struct perf_cpu cpu)
> --
> 2.34.1
>

Reviewed-by: Mike Leach <mike.leach@...aro.org>

--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK