linux-kernel - Re: [PATCH 3/4] perf mem amd: Fix perf_pmus__num_mem

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Message-ID: <CAP-5=fW0R2Dkwvw0twdzL5GrLy6jy0CXmFHYCsZtC8UQnZ4mVQ@mail.gmail.com>
Date:   Tue, 13 Jun 2023 08:25:58 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     acme@...nel.org, jolsa@...nel.org, namhyung@...nel.org,
        mark.rutland@....com, peterz@...radead.org,
        adrian.hunter@...el.com, kan.liang@...ux.intel.com,
        james.clark@....com, alisaidi@...zon.com, leo.yan@...aro.org,
        maddy@...ux.ibm.com, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        ananth.narayan@....com, santosh.shukla@....com
Subject: Re: [PATCH 3/4] perf mem amd: Fix perf_pmus__num_mem_pmus()

On Tue, Jun 13, 2023 at 2:56 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
>
> AMD cpus does not contain hybrid cores. Also, perf mem/c2c on AMD
> internally uses IBS OP PMU, not the core PMU.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> ---
>  tools/perf/arch/x86/util/pmu.c | 15 +++++++++++++++
>  tools/perf/util/pmus.c         |  2 +-
>  2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
> index 3c0de3370d7e..8a20d28d9927 100644
> --- a/tools/perf/arch/x86/util/pmu.c
> +++ b/tools/perf/arch/x86/util/pmu.c
> @@ -14,6 +14,8 @@
>  #include "../../../util/intel-bts.h"
>  #include "../../../util/pmu.h"
>  #include "../../../util/fncache.h"
> +#include "../../../util/pmus.h"
> +#include "env.h"
>
>  struct pmu_alias {
>         char *name;
> @@ -168,3 +170,16 @@ char *pmu_find_alias_name(const char *name)
>
>         return __pmu_find_alias_name(name);
>  }
> +
> +int perf_pmus__num_mem_pmus(void)
> +{
> +       /*
> +        * AMD does not have hybrid cores and also uses IBS OP
> +        * pmu for perf mem/c2c.
> +        */
> +       if (x86__is_amd_cpu())
> +               return 1;

The code and comment seem out of sync here. For the hybrid part
perf_pmus__num_core_pmus() will yield 1 if there is no hybrid, so we
can just use perf_pmus__num_core_pmus(). For the IBS OP part, does
that mean that AMD should have 2 mem pmus? Or is IBS OP a core PMU?
Can we add this as an example in the core/other documentation in patch
1, as you've done for ARM, for clarity.

Thanks,
Ian

> +
> +       /* Intel uses core pmus for perf mem/c2c */
> +       return perf_pmus__num_core_pmus();
> +}
> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> index e505d2fef828..0ed943932945 100644
> --- a/tools/perf/util/pmus.c
> +++ b/tools/perf/util/pmus.c
> @@ -240,7 +240,7 @@ const struct perf_pmu *perf_pmus__pmu_for_pmu_filter(const char *str)
>         return NULL;
>  }
>
> -int perf_pmus__num_mem_pmus(void)
> +int __weak perf_pmus__num_mem_pmus(void)
>  {
>         /* All core PMUs are for mem events. */
>         return perf_pmus__num_core_pmus();
> --
> 2.40.1
>