linux-kernel - Re: [PATCH 2/2] perf vendor events arm64 AmpereOneX: Fix frontend

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Message-ID: <880bebc4-5a59-451e-beb2-60cee9a3efd5@linaro.org>
Date: Tue, 18 Mar 2025 10:47:02 +0000
From: James Clark <james.clark@...aro.org>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...nel.org>, Ian Rogers <irogers@...gle.com>,
 John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
 Mike Leach <mike.leach@...aro.org>, Leo Yan <leo.yan@...ux.dev>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/2] perf vendor events arm64 AmpereOneX: Fix
 frontend_bound calculation



On 13/03/2025 8:15 pm, Ilkka Koskinen wrote:
> frontend_bound metrics was miscalculated due to different scaling in
> a couple of metrics it depends on. Change the scaling to match with
> AmpereOne.
> 
> Fixes: 16438b652b46 ("perf vendor events arm64 AmpereOneX: Add core PMU events and metrics")
> Signed-off-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
> ---
>   .../arch/arm64/ampere/ampereonex/metrics.json          | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/pmu-events/arch/arm64/ampere/ampereonex/metrics.json b/tools/perf/pmu-events/arch/arm64/ampere/ampereonex/metrics.json
> index c5d1d22bd034..5228f94a793f 100644
> --- a/tools/perf/pmu-events/arch/arm64/ampere/ampereonex/metrics.json
> +++ b/tools/perf/pmu-events/arch/arm64/ampere/ampereonex/metrics.json
> @@ -229,19 +229,19 @@
>       },
>       {
>           "MetricName": "slots_lost_misspeculation_fraction",
> -        "MetricExpr": "(OP_SPEC - OP_RETIRED) / (CPU_CYCLES * #slots)",
> +        "MetricExpr": "100 * (OP_SPEC - OP_RETIRED) / (CPU_CYCLES * #slots)",
>           "BriefDescription": "Fraction of slots lost due to misspeculation",
>           "DefaultMetricgroupName": "TopdownL1",
>           "MetricGroup": "Default;TopdownL1",
> -        "ScaleUnit": "100percent of slots"
> +        "ScaleUnit": "1percent of slots"
>       },
>       {
>           "MetricName": "retired_fraction",
> -        "MetricExpr": "OP_RETIRED / (CPU_CYCLES * #slots)",
> +        "MetricExpr": "100 * OP_RETIRED / (CPU_CYCLES * #slots)",
>           "BriefDescription": "Fraction of slots retiring, useful work",
>           "DefaultMetricgroupName": "TopdownL1",
>           "MetricGroup": "Default;TopdownL1",
> -        "ScaleUnit": "100percent of slots"
> +        "ScaleUnit": "1percent of slots"

I never considered that ScaleUnit could be an issue when the metric was 
included in other metrics with different scales. Seems like an easy trap.

Reviewed-by: James Clark <james.clark@...aro.org>