linux-kernel - Re: [PATCH v5 2/6] perf vendor events arm64: Add TLB metrics for neoverse-n2

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Date:   Wed, 4 Jan 2023 16:40:13 +0800
From:   Jing Zhang <renyu.zj@...ux.alibaba.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     John Garry <john.g.garry@...cle.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>,
        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 2/6] perf vendor events arm64: Add TLB metrics for
 neoverse-n2



在 2023/1/4 下午1:21, Jing Zhang 写道:
> 
> 
> 在 2023/1/4 上午1:14, Ian Rogers 写道:
>> On Tue, Jan 3, 2023 at 3:39 AM Jing Zhang <renyu.zj@...ux.alibaba.com> wrote:
>>>
>>> Add TLB related metrics.
>>>
>>> Signed-off-by: Jing Zhang <renyu.zj@...ux.alibaba.com>
>>> Acked-by: Ian Rogers <irogers@...gle.com>
>>> ---
>>>  .../arch/arm64/arm/neoverse-n2/metrics.json        | 49 ++++++++++++++++++++++
>>>  1 file changed, 49 insertions(+)
>>>
>>> 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 c126f1bc..8a74e07 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
>>> @@ -26,5 +26,54 @@
>>>          "MetricGroup": "TopdownL1",
>>>          "MetricName": "backend_bound",
>>>          "ScaleUnit": "100%"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "L1D_TLB_REFILL / L1D_TLB",
>>> +        "BriefDescription": "The rate of L1D TLB refill to the overall L1D TLB lookups",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "l1d_tlb_miss_rate",
>>> +        "ScaleUnit": "100%"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "L1I_TLB_REFILL / L1I_TLB",
>>> +        "BriefDescription": "The rate of L1I TLB refill to the overall L1I TLB lookups",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "l1i_tlb_miss_rate",
>>> +        "ScaleUnit": "100%"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "L2D_TLB_REFILL / L2D_TLB",
>>> +        "BriefDescription": "The rate of L2D TLB refill to the overall L2D TLB lookups",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "l2_tlb_miss_rate",
>>> +        "ScaleUnit": "100%"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "DTLB_WALK / INST_RETIRED * 1000",
>>> +        "BriefDescription": "The rate of TLB Walks per kilo instructions for data accesses",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "dtlb_mpki",
>>> +        "ScaleUnit": "MPKI"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "DTLB_WALK / L1D_TLB",
>>> +        "BriefDescription": "The rate of DTLB Walks to the overall L1D TLB lookups",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "dtlb_walk_rate",
>>> +        "ScaleUnit": "100%"
>>> +    },
>>> +    {
>>> +        "MetricExpr": "ITLB_WALK / INST_RETIRED * 1000",
>>> +        "BriefDescription": "The rate of TLB Walks per kilo instructions for instruction accesses",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "itlb_mpki",
>>> +        "ScaleUnit": "MPKI"
>>
>> Did you test this? IIRC if there is no number in the ScaleUnit then
>> the scale factor becomes 0 and the metric value is always multiplied
>> by zero. Perhaps:
>>
>> "MetricName": "itlb_miss_rate",
>> "MetricExpr": "ITLB / INST_RETIRED"
>> "ScaleUnit": "1000MPKI"
>>
>> Thanks,
>> Ian
>>
> 
> You are absolutely right, I only tested TLB metrics. Sorry for not double checking. I will repost the corrected patches.
> 

I rethought it. I want to change the ScaleUnit to "1MPKI" and keep the MetricExpr multiplied by 1000,
so that the "MetricExpr" expresses the value of per kilo instruciton, which can be consistent with the
description in "BriefDescription". Like:
   {
        "MetricExpr": "DTLB_WALK / INST_RETIRED * 1000",
        "BriefDescription": "The rate of TLB Walks per kilo instructions for data accesses",
        "MetricGroup": "TLB",
        "MetricName": "dtlb_mpki",
        "ScaleUnit": "1MPKI"
    },


In addition, I think it is more reasonable for ScaleUnit to have a default scale factor of 1 when there
is no number. I want to try to fix this bug.

Ian, what's your opnion?


>>> +    },
>>> +    {
>>> +        "MetricExpr": "ITLB_WALK / L1I_TLB",
>>> +        "BriefDescription": "The rate of ITLB Walks to the overall L1I TLB lookups",
>>> +        "MetricGroup": "TLB",
>>> +        "MetricName": "itlb_walk_rate",
>>> +        "ScaleUnit": "100%"
>>>      }
>>>  ]
>>> --
>>> 1.8.3.1
>>>