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Subject: Re: [PATCH v2 0/7] perf arm-spe: Enable timestamp
To:     Leo Yan <leo.yan@linaro.org>, Al Grant <Al.Grant@arm.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        James Clark <James.Clark@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <Mark.Rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20210403072346.30430-1-leo.yan@linaro.org>
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 <20210407131529.GA585163@leoy-ThinkPad-X240s>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Message-ID: <0016288d-a490-f8fb-f108-0969b946494e@intel.com>
Date:   Wed, 7 Apr 2021 16:28:40 +0300
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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.