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

[Ian Rogers]

On Thu, Nov 24, 2022 at 9:15 AM Jing Zhang <renyu.zj@xxxxxxxxxxxxxxxxx> wrote:
>
> Add PE utilization related metrics.
>
> Signed-off-by: Jing Zhang <renyu.zj@xxxxxxxxxxxxxxxxx>
> ---
>  .../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
>