[PATCH v6 1/2] perf pmu intel: Generalize SNC cpumask adjustment for multiple platforms

[PATCH v6 1/2] perf pmu intel: Generalize SNC cpumask adjustment for multiple platforms

[Chun-Tse Shao]

Prepare for supporting more Intel platforms with sub-NUMA clustering by
generalizing the GNR specific logic.

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
v6:
  Make string literal.
  Add SPR into SNC2.

v5: lore.kernel.org/20260407203918.3178481-1-ctshao@google.com/
  Split patch.

v4: lore.kernel.org/20260402205300.1953706-1-ctshao@google.com
  Rebase.

v3: lore.kernel.org/20260212223942.3832857-1-ctshao@google.com
  Fix a typo.

v2: lore.kernel.org/20260205232220.1980168-1-ctshao@google.com
  Split EMR and GNR in the SNC2 IMC cpu map.

v1: lore.kernel.org/20260108184430.1210223-1-ctshao@google.com

 tools/perf/arch/x86/util/pmu.c | 46 +++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 17 deletions(-)

diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
index 7c9d238922a6..b8fab260c423 100644
--- a/tools/perf/arch/x86/util/pmu.c
+++ b/tools/perf/arch/x86/util/pmu.c
@@ -22,20 +22,30 @@
 #include "util/env.h"
 #include "util/header.h"

-static bool x86__is_intel_graniterapids(void)
+#define GENUINE_INTEL_GNR "GenuineIntel-6-A[DE]"
+
+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_snc_supported) {

-	if (!checked_if_graniterapids) {
-		const char *graniterapids_cpuid = "GenuineIntel-6-A[DE]";
+		/* Graniterapids supports SNC configuration. */
+		static const char *const supported_cpuids[] = {
+			GENUINE_INTEL_GNR, /* 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)
@@ -132,8 +142,8 @@ 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;

@@ -156,11 +166,12 @@ 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;
 	}
-	return snc_map[imc_num];
+
+	return snc_map[imc_num % snc_map_len];
 }

 static int uncore_cha_imc_compute_cpu_adjust(int pmu_snc)
@@ -200,7 +211,7 @@ 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
@@ -300,11 +311,12 @@ 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);
 		}
 	}
 }
--
2.54.0.669.g59709faab0-goog

[PATCH v6 2/2] perf pmu intel: Adjust cpumasks for sub-NUMA clusters on Sapphire Rapids and Emerald Rapids

[Chun-Tse Shao]

Similar to GNR [1], Sapphire Rapids and Emerald Rapids support sub-NUMA
clusters as well. Adjust cpumasks using the same logic as GNR in [1].

Tested on Emerald Rapids with SNC2 enabled:
  $ perf stat --per-node -e 'UNC_CHA_CLOCKTICKS,UNC_M_CLOCKTICKS' -a -- sleep 1

   Performance counter stats for 'system wide':

  N0       30        72125876670      UNC_CHA_CLOCKTICKS
  N0        4         8815163648      UNC_M_CLOCKTICKS
  N1       30        72124958844      UNC_CHA_CLOCKTICKS
  N1        4         8815014974      UNC_M_CLOCKTICKS
  N2       30        72121049022      UNC_CHA_CLOCKTICKS
  N2        4         8814592626      UNC_M_CLOCKTICKS
  N3       30        72117133854      UNC_CHA_CLOCKTICKS
  N3        4         8814012840      UNC_M_CLOCKTICKS

         1.001574118 seconds time elapsed

[1] lore.kernel.org/20250515181417.491401-1-irogers@google.com

Reviewed-by: Zide Chen <zide.chen@intel.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
 tools/perf/arch/x86/util/pmu.c | 60 ++++++++++++++++++++++++----------
 1 file changed, 42 insertions(+), 18 deletions(-)

diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
index b8fab260c423..09caec0a32a5 100644
--- a/tools/perf/arch/x86/util/pmu.c
+++ b/tools/perf/arch/x86/util/pmu.c
@@ -22,6 +22,8 @@
 #include "util/env.h"
 #include "util/header.h"

+#define GENUINE_INTEL_SPR "GenuineIntel-6-8F"
+#define GENUINE_INTEL_EMR "GenuineIntel-6-CF"
 #define GENUINE_INTEL_GNR "GenuineIntel-6-A[DE]"

 static bool x86__is_snc_supported(void)
@@ -31,8 +33,10 @@ static bool x86__is_snc_supported(void)

 	if (!checked_if_snc_supported) {

-		/* Graniterapids supports SNC configuration. */
+		/* Sapphirerapids Emeraldrapids Graniterapids support SNC configuration. */
 		static const char *const supported_cpuids[] = {
+			GENUINE_INTEL_SPR, /* Sapphirerapids */
+			GENUINE_INTEL_EMR, /* Emeraldrapids */
 			GENUINE_INTEL_GNR, /* Graniterapids */
 		};
 		char *cpuid = get_cpuid_str((struct perf_cpu){0});
@@ -142,23 +146,43 @@ 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};
-	const u8 snc3_map[] = {1, 1, 0, 0, 2, 2};
-	const u8 *snc_map;
-	size_t snc_map_len;
-
-	switch (snc_nodes) {
-	case 2:
-		snc_map = snc2_map;
-		snc_map_len = ARRAY_SIZE(snc2_map);
-		break;
-	case 3:
-		snc_map = snc3_map;
-		snc_map_len = ARRAY_SIZE(snc3_map);
-		break;
-	default:
-		/* Error or no lookup support for SNC with >3 nodes. */
-		return 0;
+	char *cpuid;
+	static const u8 spr_emr_snc2_map[] = { 0, 0, 1, 1 };
+	static const u8 gnr_snc2_map[] = { 1, 1, 0, 0 };
+	static const u8 snc3_map[] = { 1, 1, 0, 0, 2, 2 };
+	static const u8 *snc_map;
+	static size_t snc_map_len;
+
+	/* snc_map is not inited yet. We only look up once to avoid expensive operations. */
+	if (!snc_map) {
+		switch (snc_nodes) {
+		case 2:
+			cpuid = get_cpuid_str((struct perf_cpu){ 0 });
+			if (cpuid) {
+				if (strcmp_cpuid_str(GENUINE_INTEL_SPR, cpuid) == 0 ||
+				    strcmp_cpuid_str(GENUINE_INTEL_EMR, cpuid) == 0) {
+					snc_map = spr_emr_snc2_map;
+					snc_map_len = ARRAY_SIZE(spr_emr_snc2_map);
+				} else if (strcmp_cpuid_str(GENUINE_INTEL_GNR, cpuid) == 0) {
+					snc_map = gnr_snc2_map;
+					snc_map_len = ARRAY_SIZE(gnr_snc2_map);
+				}
+				free(cpuid);
+			}
+			break;
+		case 3:
+			snc_map = snc3_map;
+			snc_map_len = ARRAY_SIZE(snc3_map);
+			break;
+		default:
+			/* Error or no lookup support for SNC with >3 nodes. */
+			return 0;
+		}
+
+		if (!snc_map) {
+			pr_warning("Unexpected: can not find snc map config");
+			return 0;
+		}
 	}

 	/* Compute SNC for PMU. */
--
2.54.0.669.g59709faab0-goog

Re: [PATCH v6 1/2] perf pmu intel: Generalize SNC cpumask adjustment for multiple platforms

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] The bounds check for `imc_num` incorrectly limits the maximum IMC number based on the number of active sockets, causing valid IMC PMUs to be rejected and leaving their cpumasks unadjusted on single-socket systems.
- [High] A divide-by-zero crash can occur when computing `cha_snc` due to an unhandled edge case where the number of discovered CHA PMUs is less than the calculated `snc_nodes`.
--

commit c91c5bd96c1936822e95d0f574b8f633d5afb4c1
Author: Chun-Tse Shao <ctshao@google.com>

perf pmu intel: Generalize SNC cpumask adjustment for multiple platforms

Prepare for supporting more Intel platforms with sub-NUMA clustering by
generalizing the GNR specific logic.

> diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
> index 7c9d238922a6c..b8fab260c4238 100644
> --- a/tools/perf/arch/x86/util/pmu.c
> +++ b/tools/perf/arch/x86/util/pmu.c

[ ... ]

> @@ -156,11 +166,12 @@ 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)) {

Will this condition incorrectly limit the maximum IMC number based on the
number of active sockets?

The expression perf_cpu_map__nr(pmu->cpus) represents the number of active
sockets, meaning it will evaluate to 1 on a single-socket system. In an
SNC3 configuration where snc_map_len is 6, this would limit imc_num to
less than 6.

Could this cause single-socket systems to wrongly reject imc_num >= 6,
given that the hardware might still expose 12 IMC blocks on that socket?
If so, processing uncore_imc_6 through uncore_imc_11 would trigger the
"Unexpected IMC" warning and skip the necessary cpumask adjustments.

(Note that subsequent patches in the series, such as "perf pmu intel:
Adjust cpumasks for sub-NUMA clusters on Sapphire Rapids and Emerald
Rapids", do not appear to resolve this bounds check).

>  		pr_warning("Unexpected IMC %d for SNC%d mapping\n", imc_num, snc_nodes);
>  		return 0;
>  	}

[ ... ]

> @@ -300,11 +311,12 @@ 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);

Is it possible for a divide-by-zero to occur when this generalized
adjustment logic invokes uncore_cha_snc()?

If a system or container restricts access to sysfs and exposes fewer CHA
devices, or if testing under a fake PMU environment, the dynamically
determined num_cha could be less than the calculated snc_nodes.

In uncore_cha_snc(), the code performs:

chas_per_node = num_cha / snc_nodes;

And later evaluates:

cha_snc = cha_num / chas_per_node;

Could the initial integer division result in chas_per_node = 0, causing
an unhandled crash when evaluating cha_snc?

> +			else if (strstarts(pmu->name, "uncore_imc_") &&
> +				 !strstarts(pmu->name, "uncore_imc_free_running"))
> +				uncore_cha_imc_adjust_cpumask_for_snc(pmu, /*cha=*/false);
>  		}
>  	}
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260515172710.428474-1-ctshao@google.com?part=1

Re: [PATCH v6 2/2] perf pmu intel: Adjust cpumasks for sub-NUMA clusters on Sapphire Rapids and Emerald Rapids

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Missing IMC cpumask adjustment and silent failure for SNC4 configurations on Sapphire Rapids.
--

commit 312ea8a1894ae6a4d9318072afccaf0abbbb29bd
Author: Chun-Tse Shao <ctshao@google.com>

perf pmu intel: Adjust cpumasks for sub-NUMA clusters on Sapphire Rapids and Emerald Rapids

This commit adjusts the cpumasks for sub-NUMA clusters on Sapphire Rapids
and Emerald Rapids processors. It updates the detection logic and the
mapping arrays to support SNC configurations for these architectures.

> diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
> index b8fab260c4238..09caec0a32a57 100644
> --- a/tools/perf/arch/x86/util/pmu.c
> +++ b/tools/perf/arch/x86/util/pmu.c
[ ... ]
> @@ -142,23 +146,43 @@ 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();
[ ... ]
> +	/* snc_map is not inited yet. We only look up once to avoid expensive operations. */
> +	if (!snc_map) {
> +		switch (snc_nodes) {
> +		case 2:
[ ... ]
> +			break;
> +		case 3:
> +			snc_map = snc3_map;
> +			snc_map_len = ARRAY_SIZE(snc3_map);
> +			break;
> +		default:
> +			/* Error or no lookup support for SNC with >3 nodes. */
> +			return 0;

Sapphire Rapids natively supports 4-way sub-NUMA clustering, which would
make snc_nodes evaluate to 4. Does this regression silently skip IMC
cpumask adjustments for SNC4 configurations?

Because this default case returns 0 immediately, it entirely bypasses the
newly added warning block below.

> +		}
> +
> +		if (!snc_map) {
> +			pr_warning("Unexpected: can not find snc map config");
> +			return 0;
> +		}

Could this leave users unaware that the IMC PMUs are unmapped, even though
CHA PMUs are correctly adjusted for SNC4 elsewhere?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260515172710.428474-1-ctshao@google.com?part=2