linux-kernel - Re: [PATCH v2 1/5] perf arm-spe: Define metadata header version 2

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Message-ID: <f6a90906-6855-4524-9ff8-62099cbdb863@arm.com>
Date: Fri, 27 Sep 2024 09:05:36 +0100
From: Leo Yan <leo.yan@....com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
 James Clark <james.clark@...aro.org>, Mike Leach <mike.leach@...aro.org>,
 Will Deacon <will@...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-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] perf arm-spe: Define metadata header version 2

On 9/27/24 07:32, Namhyung Kim wrote:

[...]

>> diff --git a/tools/perf/util/arm-spe.h b/tools/perf/util/arm-spe.h
>> index 4f4900c18f3e..5416d4e1d15f 100644
>> --- a/tools/perf/util/arm-spe.h
>> +++ b/tools/perf/util/arm-spe.h
>> @@ -12,10 +12,46 @@
>>   enum {
>>        ARM_SPE_PMU_TYPE,
>>        ARM_SPE_PER_CPU_MMAPS,
>> +     ARM_SPE_AUXTRACE_V1_PRIV_MAX,
>> +};
>> +
>> +#define ARM_SPE_AUXTRACE_V1_PRIV_SIZE        \
>> +     (ARM_SPE_AUXTRACE_V1_PRIV_MAX * sizeof(u64))
>> +
>> +enum {
>> +     /*
>> +      * The old metadata format (defined above) does not include a
>> +      * field for version number. Version 1 is reserved and starts
>> +      * from version 2.
>> +      */
>> +     ARM_SPE_HEADER_VERSION,
>> +     /* Number of sizeof(u64) */
>> +     ARM_SPE_HEADER_SIZE,
>> +     /* PMU type shared by CPUs */
>> +     ARM_SPE_SHARED_PMU_TYPE,
>> +     /* Number of CPUs */
>> +     ARM_SPE_CPUS_NUM,
>>        ARM_SPE_AUXTRACE_PRIV_MAX,
>>   };
> 
> Why don't you define something like struct arm_spe_header_v2 ?

Here the target is to make metadata to be self-described and can be
easily extended for new version (but I would not expect updating header
will happen frequently).

The fields ARM_SPE_HEADER_VERSION and ARM_SPE_HEADER_SIZE give a
header version and a header size. This allows us to easily extend new
enum items for new header. A benefit is we can use general code for
decoding because we don't need to process structure for a specific
version.

Thanks for review!

Leo