linux-kernel - Re: [PATCH v2 0/7] perf arm-spe: Enable timestamp

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Message-ID: <0016288d-a490-f8fb-f108-0969b946494e@intel.com>
Date:   Wed, 7 Apr 2021 16:28:40 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Leo Yan <leo.yan@...aro.org>, Al Grant <Al.Grant@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        James Clark <James.Clark@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <Mark.Rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/7] perf arm-spe: Enable timestamp

On 7/04/21 4:15 pm, Leo Yan wrote:
> Hi Al,
> 
> On Tue, Apr 06, 2021 at 09:38:32AM +0000, Al Grant wrote:
> 
> [...]
> 
>>> This patch set is to enable timestamp for Arm SPE trace.  It reads out TSC
>>> parameters from mmap page and stores into auxtrace info structure;
>>
>> Why not synthesize a PERF_RECORD_TIME_CONV - isn't that specifically to
>> capture the TSC parameters from the mmap page? If a generic mechanism
>> exists it would be better to use it, otherwise we'll have to do this again for
>> future trace formats.
> 
> Good point!  Actually "perf record" tool has synthesized event
> PERF_RECORD_TIME_CONV.  This patch series is studying the
> implementation from Intel-PT, so the question is why the existed
> implementations (like Intel-PT, Intel-BTS) don't directly use
> PERF_RECORD_TIME_CONV for retriving TSC parameters.

PERF_RECORD_TIME_CONV was added later because the TSC information is
needed by jitdump.