linux-kernel - Re: [PATCH v5 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2

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Message-ID: <7aa225df-af25-a6be-9bef-c965488ba43a@oracle.com>
Date:   Wed, 4 Jan 2023 17:26:19 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Jing Zhang <renyu.zj@...ux.alibaba.com>,
        Ian Rogers <irogers@...gle.com>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        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>
Subject: Re: [PATCH v5 1/6] perf vendor events arm64: Add topdown L1 metrics
 for neoverse-n2

On 04/01/2023 05:05, Jing Zhang wrote:
> 
> 
> 在 2023/1/3 下午7:52, John Garry 写道:
>> On 03/01/2023 11:39, Jing Zhang wrote:
>>> The formula of topdown L1 on neoverse-n2 is from ARM sbsa7.0 platform
>>> design document [0], D37-38.
>>
>> I think that I mentioned this before - if the these metrics are coming from an sbsa doc, then they are standard. As such, we can make them "arch std events" and put them in a common json such as sbsa.json, so that other cores may reuse.
>>
>> You don't strictly have to do do this now, but it would be better.
>>
> 
> Hi John,

Hi Jing,

> 
> I would really like to do this, but as discussed earlier, slot is different on each architectures.
> If I do not specify the value of the slot in sbsa.json, then in the json file of n2/v1, I need to
> overwrite each topdown "MetricExpr". In other words, the metrics placed in the sbsa.json file only
> reuse "BriefDescription", "MetricGroup" and "ScaleUnit". So I'm not sure if it's acceptable?

I don't see a lot of value in that really.

However, for this value of slot, isn't this discoverable from a system 
register per core? Quoting the sbsa: "The IMPLEMENTATION DEFINED 
constant SLOTS is discoverable from the system register 
PMMIR_EL1.SLOTS." Did you consider how this could be used?

> 
> In addition, James mentioned that if the units and names and group names of different architectures
> are not unified, it will become complicated.
> 

Thanks,
John