Re: [PATCH 2/2] perf/x86/amd/core: Add ref-cycles event for Zen 4 and later

[Ian Rogers]

On Mon, Mar 25, 2024 at 12:48 AM Sandipan Das <sandipan.das@xxxxxxx> wrote:
>
> Add the "ref-cycles" event for AMD processors based on Zen 4 and later
> microarchitectures. The backing event is based on PMCx120 which counts
> cycles not in halt state in P0 frequency (same as MPERF).

This reminds me that we lack smi cost and an smi_cycles metric for
AMD, here is an Intel one:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json?h=perf-tools-next#n274
The metric uses APERF but runs with freeze_on_smi set:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/builtin-stat.c?h=perf-tools-next#n2115
so the delta between cycles and aperf is the cycles in SMI. It would
be great if we could get something similar on AMD.

> Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>

Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
>  arch/x86/events/amd/core.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index afe4a809f2ed..685bfa860d67 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -273,8 +273,23 @@ static const u64 amd_zen2_perfmon_event_map[PERF_COUNT_HW_MAX] =
>         [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x00a9,
>  };
>
> +static const u64 amd_zen4_perfmon_event_map[PERF_COUNT_HW_MAX] =
> +{
> +       [PERF_COUNT_HW_CPU_CYCLES]              = 0x0076,
> +       [PERF_COUNT_HW_INSTRUCTIONS]            = 0x00c0,
> +       [PERF_COUNT_HW_CACHE_REFERENCES]        = 0xff60,
> +       [PERF_COUNT_HW_CACHE_MISSES]            = 0x0964,
> +       [PERF_COUNT_HW_BRANCH_INSTRUCTIONS]     = 0x00c2,
> +       [PERF_COUNT_HW_BRANCH_MISSES]           = 0x00c3,
> +       [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x00a9,
> +       [PERF_COUNT_HW_REF_CPU_CYCLES]          = 0x100000120,
> +};
> +
>  static u64 amd_pmu_event_map(int hw_event)
>  {
> +       if (cpu_feature_enabled(X86_FEATURE_ZEN4) || boot_cpu_data.x86 >= 0x1a)
> +               return amd_zen4_perfmon_event_map[hw_event];
> +
>         if (cpu_feature_enabled(X86_FEATURE_ZEN2) || boot_cpu_data.x86 >= 0x19)
>                 return amd_zen2_perfmon_event_map[hw_event];
>
> --
> 2.34.1
>