linux-kernel - Re: [PATCH v3 5/6] perf vendor events arm64: Add PE utilization metrics for neoverse-n2

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Message-ID: <CAP-5=fV0WSTK=MT6K2nqsqYT6xCTg7Pv_rXahHFeRhV0ZHCiEQ@mail.gmail.com>
Date:   Wed, 30 Nov 2022 10:58:37 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Jing Zhang <renyu.zj@...ux.alibaba.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 v3 5/6] perf vendor events arm64: Add PE utilization
 metrics for neoverse-n2

On Thu, Nov 24, 2022 at 9:15 AM Jing Zhang <renyu.zj@...ux.alibaba.com> wrote:
>
> Add PE utilization related metrics.
>
> Signed-off-by: Jing Zhang <renyu.zj@...ux.alibaba.com>
> ---
>  .../arch/arm64/arm/neoverse-n2/metrics.json        | 45 ++++++++++++++++++++++
>  1 file changed, 45 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 23c7d62..7b54819 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
> @@ -189,5 +189,50 @@
>          "MetricGroup": "Branch",
>          "MetricName": "branch_miss_pred_rate",
>          "ScaleUnit": "100%"
> +    },
> +    {
> +        "MetricExpr": "instructions / CPU_CYCLES",
> +        "PublicDescription": "The average number of instructions executed for each cycle.",
> +        "BriefDescription": "Instructions per cycle",
> +        "MetricGroup": "PEutilization",
> +        "MetricName": "ipc"
> +    },

A related useful metric is percentage of peak, so if the peak IPC is 8
(usually a constant related to the number of functional units) then
you can just compute the ratio of IPC with this.

> +    {
> +        "MetricExpr": "INST_RETIRED / CPU_CYCLES",
> +        "PublicDescription": "Architecturally executed Instructions Per Cycle (IPC)",
> +        "BriefDescription": "Architecturally executed Instructions Per Cycle (IPC)",


The duplicated descriptions are unnecessary. Drop the public one for
consistency with what we do for Intel:
https://github.com/intel/perfmon/blob/main/scripts/create_perf_json.py#L299

> +        "MetricGroup": "PEutilization",
> +        "MetricName": "retired_ipc"
> +    },
> +    {
> +        "MetricExpr": "INST_SPEC / CPU_CYCLES",
> +        "PublicDescription": "Speculatively executed Instructions Per Cycle (IPC)",
> +        "BriefDescription": "Speculatively executed Instructions Per Cycle (IPC)",
> +        "MetricGroup": "PEutilization",
> +        "MetricName": "spec_ipc"
> +    },
> +    {
> +        "MetricExpr": "OP_RETIRED / OP_SPEC",
> +        "PublicDescription": "Fraction of operations retired",
> +        "BriefDescription": "Fraction of operations retired",

Would instructions be clearer than operations here?

> +        "MetricGroup": "PEutilization",
> +        "MetricName": "retired_rate",
> +        "ScaleUnit": "100%"
> +    },
> +    {
> +        "MetricExpr": "1 - OP_RETIRED / OP_SPEC",

Should OP_RETIRED be greater than OP_SPEC? In which case won't this
metric be negative?

> +        "PublicDescription": "Fraction of operations wasted",
> +        "BriefDescription": "Fraction of operations wasted",
> +        "MetricGroup": "PEutilization",
> +        "MetricName": "wasted_rate",
> +        "ScaleUnit": "100%"
> +    },
> +    {
> +        "MetricExpr": "OP_RETIRED / OP_SPEC * (1 - (STALL_SLOT - CPU_CYCLES) / (CPU_CYCLES * 5))",
> +        "PublicDescription": "Utilization of CPU",
> +        "BriefDescription": "Utilization of CPU",

Some more detail in the description would be useful.

> +        "MetricGroup": "PEutilization",
> +        "MetricName": "cpu_utilization",
> +        "ScaleUnit": "100%"
>      }
>  ]
> --
> 1.8.3.1
>