linux-kernel - Re: [PATCH v3] perf jevents: Parse metrics during conversion

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Date:   Mon, 5 Dec 2022 12:56:45 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ian Rogers <irogers@...gle.com>
Cc:     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@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v3] perf jevents: Parse metrics during conversion

On 05/12/2022 12:53, Arnaldo Carvalho de Melo wrote:
> Em Wed, Nov 30, 2022 at 07:41:38PM -0800, Ian Rogers escreveu:
>> Currently the 'MetricExpr' json value is passed from the json
>> file to the pmu-events.c. This change introduces an expression
>> tree that is parsed into. The parsing is done largely by using
>> operator overloading and python's 'eval' function. Two advantages
>> in doing this are:
>>
>> 1) Broken metrics fail at compile time rather than relying on
>>     `perf test` to detect. `perf test` remains relevant for checking
>>     event encoding and actual metric use.
>>
>> 2) The conversion to a string from the tree can minimize the metric's
>>     string size, for example, preferring 1e6 over 1000000, avoiding
>>     multiplication by 1 and removing unnecessary whitespace. On x86
>>     this reduces the string size by 3,050bytes (0.07%).
>>
>> In future changes it would be possible to programmatically
>> generate the json expressions (a single line of text and so a
>> pain to write manually) for an architecture using the expression
>> tree. This could avoid copy-pasting metrics for all architecture
>> variants.
>>
>> Signed-off-by: Ian Rogers<irogers@...gle.com>
>>
>> v3. Avoids generic types on standard types like set that aren't
>>      supported until Python 3.9, fixing an issue with Python 3.6
>>      reported-by John Garry. v3 also fixes minor pylint issues and adds
>>      a call to Simplify on the read expression tree.
> Cool, John looked reviewed it (may I add the tag?). Applying to my local
> tree, will do some light testing.

Actually I just got as far as testing v2 (which gave rise to this v3). I 
will look at it further today.

Thanks,
John