linux-kernel - Re: [RFC PATCH 2/5] perf jevents: add support for arch recommended events

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Date:   Fri, 15 Dec 2017 11:22:50 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <namhyung@...nel.org>,
        <ak@...ux.intel.com>, <wcohen@...hat.com>, <will.deacon@....com>,
        <ganapatrao.kulkarni@...ium.com>, <catalin.marinas@....com>,
        <mark.rutland@....com>, <xuwei5@...ilicon.com>,
        <linuxarm@...wei.com>, <zhangshaokun@...ilicon.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/5] perf jevents: add support for arch recommended
 events

>> Actually having a scalable JSON standard format for pmu events, which allows
>> us to define common events per architecture / vendor and reference them per
>> platform JSON could be useful.
>>
>> Here we're dealing with trade-off between duplication (simplicity) vs
>> complexity (or over-engineering).
>
> understood, but as I said we already are ok with duplicates,
> if it's reasonable size as is for x86 now..  how much amount
> are we talking about for arm?
>

Hi Jirka,

When you say reasonable size for x86, I ran a string duplication finder 
on the x86 JSONs and the results show a huge amount of duplication. 
Please check this:
https://gist.githubusercontent.com/johnpgarry/68bc87e823ae2ce0f7b475b4e55e5795/raw/f4cea138999d8b34151b9586d733592e01774d7a/x86%2520JSON%2520duplication

Extract:
"Found a 65 line (311 tokens) duplication in the following files:
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/ivybridge/ivb-metrics.json
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/ivytown/ivt-metrics.json
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/broadwell/bdw-metrics.json
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
Starting at line 76 of 
/linux/tools/perf/pmu-events/arch/x86/jaketown/jkt-metrics.json
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/skylake/skl-metrics.json
Starting at line 76 of 
/linux/tools/perf/pmu-events/arch/x86/sandybridge/snb-metrics.json
Starting at line 100 of 
/linux/tools/perf/pmu-events/arch/x86/broadwellx/bdx-metrics.json"

Won't this all potentially have a big maintainence cost?

For example, I saw multiple JSON update patches which look identical:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/tools/perf/pmu-events/arch/x86?h=v4.15-rc3&id=7347bba5552f479d4292ffd008d18d41a965f021

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/tools/perf/pmu-events/arch/x86?h=v4.15-rc3&id=984d91f4c62f64026cbfef51f609971025934cec

I just don't know how this schema scales with more archs and more 
platforms supported. It's just early days now...

Regards,
John

> jirka
>
> .
>