Re: [PATCH v5 1/2] perf pmu intel: Generalize SNC cpumask adjustment for multiple platforms

[Namhyung Kim]

Hello,

On Tue, Apr 07, 2026 at 01:38:42PM -0700, Chun-Tse Shao wrote:
> Prepare for supporting more Intel platforms with sub-NUMA clustering by
> generalizing the GNR specific logic.
> 
> Signed-off-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>
> ---
> v5:
>   Split patch.
> 
> v4: lore.kernel.org/20260402205300.1953706-1-ctshao@xxxxxxxxxx
>   Rebase.
> 
> v3: lore.kernel.org/20260212223942.3832857-1-ctshao@xxxxxxxxxx
>   Fix a typo.
> 
> v2: lore.kernel.org/20260205232220.1980168-1-ctshao@xxxxxxxxxx
>   Split EMR and GNR in the SNC2 IMC cpu map.
> 
> v1: lore.kernel.org/20260108184430.1210223-1-ctshao@xxxxxxxxxx
> 
>  tools/perf/arch/x86/util/pmu.c | 44 +++++++++++++++++++++-------------
>  1 file changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
> index 0661e0f0b02d..938be36ec0f7 100644
> --- a/tools/perf/arch/x86/util/pmu.c
> +++ b/tools/perf/arch/x86/util/pmu.c
> @@ -23,20 +23,28 @@
>  #include "util/env.h"
>  #include "util/header.h"
> 
> -static bool x86__is_intel_graniterapids(void)
> +static bool x86__is_snc_supported(void)
>  {
> -	static bool checked_if_graniterapids;
> -	static bool is_graniterapids;
> +	static bool checked_if_snc_supported;
> +	static bool is_supported;
> 
> -	if (!checked_if_graniterapids) {
> -		const char *graniterapids_cpuid = "GenuineIntel-6-A[DE]";
> +	if (!checked_if_snc_supported) {
> +
> +		/* Graniterapids supports SNC configuration. */
> +		static const char *const supported_cpuids[] = {
> +			"GenuineIntel-6-A[DE]", /* Graniterapids */
> +		};
>  		char *cpuid = get_cpuid_str((struct perf_cpu){0});
> 
> -		is_graniterapids = cpuid && strcmp_cpuid_str(graniterapids_cpuid, cpuid) == 0;
> +		for (size_t i = 0; i < ARRAY_SIZE(supported_cpuids); i++) {
> +			is_supported = cpuid && strcmp_cpuid_str(supported_cpuids[i], cpuid) == 0;
> +			if (is_supported)
> +				break;
> +		}
>  		free(cpuid);
> -		checked_if_graniterapids = true;
> +		checked_if_snc_supported = true;
>  	}
> -	return is_graniterapids;
> +	return is_supported;
>  }
> 
>  static struct perf_cpu_map *read_sysfs_cpu_map(const char *sysfs_path)
> @@ -133,8 +141,8 @@ static int uncore_imc_snc(struct perf_pmu *pmu)
>  	// Compute the IMC SNC using lookup tables.
>  	unsigned int imc_num;
>  	int snc_nodes = snc_nodes_per_l3_cache();
> -	const u8 snc2_map[] = {1, 1, 0, 0, 1, 1, 0, 0};
> -	const u8 snc3_map[] = {1, 1, 0, 0, 2, 2, 1, 1, 0, 0, 2, 2};
> +	const u8 snc2_map[] = {1, 1, 0, 0};
> +	const u8 snc3_map[] = {1, 1, 0, 0, 2, 2};
>  	const u8 *snc_map;
>  	size_t snc_map_len;
> 
> @@ -157,11 +165,12 @@ static int uncore_imc_snc(struct perf_pmu *pmu)
>  		pr_warning("Unexpected: unable to compute IMC number '%s'\n", pmu->name);
>  		return 0;
>  	}
> -	if (imc_num >= snc_map_len) {
> +	if (imc_num >= snc_map_len * perf_cpu_map__nr(pmu->cpus)) {
>  		pr_warning("Unexpected IMC %d for SNC%d mapping\n", imc_num, snc_nodes);
>  		return 0;

Like sashiko said, I'm curious if it'd work well on 1-socket machine
which may have the same number of uncore IMC PMUs.

Zide, can you confirm?

Thanks,
Namhyung

>  	}
> -	return snc_map[imc_num];
> +
> +	return snc_map[imc_num % snc_map_len];
>  }
> 
>  static int uncore_cha_imc_compute_cpu_adjust(int pmu_snc)
> @@ -201,7 +210,7 @@ static int uncore_cha_imc_compute_cpu_adjust(int pmu_snc)
>  	return cpu_adjust[pmu_snc];
>  }
> 
> -static void gnr_uncore_cha_imc_adjust_cpumask_for_snc(struct perf_pmu *pmu, bool cha)
> +static void uncore_cha_imc_adjust_cpumask_for_snc(struct perf_pmu *pmu, bool cha)
>  {
>  	// With sub-NUMA clustering (SNC) there is a NUMA node per SNC in the
>  	// topology. For example, a two socket graniterapids machine may be set
> @@ -301,11 +310,12 @@ void perf_pmu__arch_init(struct perf_pmu *pmu)
>  				pmu->mem_events = perf_mem_events_intel_aux;
>  			else
>  				pmu->mem_events = perf_mem_events_intel;
> -		} else if (x86__is_intel_graniterapids()) {
> +		} else if (x86__is_snc_supported()) {
>  			if (strstarts(pmu->name, "uncore_cha_"))
> -				gnr_uncore_cha_imc_adjust_cpumask_for_snc(pmu, /*cha=*/true);
> -			else if (strstarts(pmu->name, "uncore_imc_"))
> -				gnr_uncore_cha_imc_adjust_cpumask_for_snc(pmu, /*cha=*/false);
> +				uncore_cha_imc_adjust_cpumask_for_snc(pmu, /*cha=*/true);
> +			else if (strstarts(pmu->name, "uncore_imc_") &&
> +				 !strstarts(pmu->name, "uncore_imc_free_running"))
> +				uncore_cha_imc_adjust_cpumask_for_snc(pmu, /*cha=*/false);
>  		}
>  	}
>  }
> --
> 2.53.0.1213.gd9a14994de-goog
>