linux-kernel - Re: [PATCH v1 3/7] perf cs-etm: Calculate per CPU metadata array size

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Date:   Mon, 11 Jan 2021 07:28:55 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Kiss <Daniel.Kiss@....com>,
        Denis Nikitin <denik@...omium.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/7] perf cs-etm: Calculate per CPU metadata array size

On 1/9/21 7:44 AM, Leo Yan wrote:
> The metadata array can be extended over time and the tool, if using the
> predefined macro (like CS_ETMV4_PRIV_MAX for ETMv4) as metadata array
> size to copy data, it can cause compatible issue within different
> versions of perf tool.
> 
> E.g. we recorded a data file with an old version tool, afterwards if
> use the new version perf tool to parse the file, since the metadata
> array has been extended and the macro CS_ETMV4_PRIV_MAX has been
> altered, if use it to parse the perf data with old format, this will
> lead to mismatch.
> 
> To maintain backward compatibility, this patch calculates per CPU
> metadata array size on the runtime, the calculation is based on the
> info stored in the data file so that it's reliable.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Looks good to me.

Acked-by: Suzuki K Poulose <suzuki.poulose@....com>