linux-kernel - Re: [External] : [RFC PATCH v2 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2

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Message-ID: <57315669-e6e7-08b8-a252-bc35d4fecc01@arm.com>
Date:   Tue, 22 Nov 2022 14:00:18 +0000
From:   James Clark <james.clark@....com>
To:     John Garry <john.g.garry@...cle.com>,
        Jing Zhang <renyu.zj@...ux.alibaba.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Kilroy <andrew.kilroy@....com>,
        Shuai Xue <xueshuai@...ux.alibaba.com>,
        Zhuo Song <zhuo.song@...ux.alibaba.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, Ian Rogers <irogers@...gle.com>
Subject: Re: [External] : [RFC PATCH v2 1/6] perf vendor events arm64: Add
 topdown L1 metrics for neoverse-n2



On 21/11/2022 17:55, John Garry wrote:
> On 21/11/2022 15:17, Jing Zhang wrote:
>> I'm sorry that I misunderstood the purpose of putting metric as
>> arch_std_event at first,
>> and now it works after the modification over your suggestion.
>>
>> But there are also a few questions:
>>
>> 1. The value of the slot in the topdownL1 is various in different
>> architectures, for example,
>> the slot is 5 on neoverse-n2. If I put topdownL1 metric as
>> arch_std_event, then I need to
>> specify the slot to 5 in n2. I can specify slot values in metric like
>> below, but is there any
>> other concise way to do this?
>>
>> diff --git
>> a/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> index 8ff1dfe..b473baf 100644
>> --- a/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> +++ b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> @@ -1,4 +1,23 @@
>> [
>> +       {
>> +               "MetricExpr": "5",
>> +               "PublicDescription": "A pipeline slot represents the
>> hardware resources needed to process one uOp",
>> +               "BriefDescription": "A pipeline slot represents the
>> hardware resources needed to process one uOp",
>> +               "MetricName": "slot"
> 
> Ehhh....I'm not sure if that is a good idea. Ian or anyone else have an
> opinion on this? It is possible to reuse metrics, so it should work, but...
> 
> One problem is that "slot" would show up as a metric, which you would
> not want.
> 
> Alternatively I was going to suggest that you can overwrite specific std
> arch event attributes. So for example of frontend_bound, you could have:

I would agree with not having this and just hard coding the 5 wherever
it's needed. Once we have a few different sets of metrics in place maybe
we can start to look at deduplication, but for now I don't see the value.

> 
> + b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
> @@ -0,0 +1,30 @@
> [
>     {
>     "ArchStdEvent": "FRONTEND_BOUND",
>         "MetricExpr": "(stall_slot_frontend - cpu_cycles) / (5 *
> cpu_cycles)",
>     },
> 
>> +       }
>> +       {
>> +               "ArchStdEvent": "FRONTEND_BOUND"
>> +       },
>> +       {
>> +               "ArchStdEvent": "BACKEND_BOUND"
>> +       },
>> +       {
>> +               "ArchStdEvent": "WASTED"
>> +       },
>> +       {
>> +               "ArchStdEvent": "RETIRING"
>> +       },
>>
>>
>> 2. Should I add the topdownL1 metric to
>> tools/perf/pmu-event/recommended.json,
>> or create a new json file to place the general metric?
> 
> It would not belong in recommended.json as that is specifically for
> arch-recommended events. It would really just depend on where the value
> comes from, i.e. arm arm or sbsa.
> 

For what we're going to publish shortly we'll be generating a
metrics.json file for each CPU. It will be autogenerated so I don't
think duplication will be an issue and I'm expecting that there will be
differences in the topdown metrics between CPUs anyway. So I would also
vote to not put it in recommended.json

>>
>> Looking forward to your reply.
>