[PATCH v3 0/3] powerpc/numa: Enable coregroup support on PowerNV

COOLING8d

Revision v3 of 2 in this series.

9 messages, 2 authors, 8d ago · open the first message on its own page

[PATCH v3 0/3] powerpc/numa: Enable coregroup support on PowerNV

From: Srikar Dronamraju <hidden>
Date: 2026-09-02 12:36:22

This series prepares cpu_to_coregroup_id() for broader use and enables
coregroup support on PowerNV when firmware exposes the required
associativity information.

The first patch cleans up find_primary_domain_index(). The second makes
cpu_to_coregroup_id() available outside PPC_SPLPAR while preserving the
existing fallback behavior. The final patch detects coregroup support
from the associativity hierarchy and uses it on PowerNV systems.

Changelog from v2: https://lkml.kernel.org/r/20260605055242.1757485-5-srikar@linux.ibm.com
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
  patch 3 to build correctly)

Changelog from v1: https://lkml.kernel.org/r/20260524010017.140408-1-srikar@linux.ibm.com
- Split into 3 patches
- Handle comments from Christophe Leroy

Srikar Dronamraju (3):
  powerpc/numa: Simplify find_primary_domain_index
  powerpc/numa: Allow cpu_to_coregroup_id without PPC_SPLPAR
  powerpc/numa: Support coregroup on PowerNV

 arch/powerpc/include/asm/topology.h | 15 +++--
 arch/powerpc/mm/numa.c              | 85 ++++++++++++++++++++++-------
 2 files changed, 71 insertions(+), 29 deletions(-)

-- 
2.43.7

[PATCH v3 1/3] powerpc/numa: Simplify find_primary_domain_index

From: Srikar Dronamraju <hidden>
Date: 2026-09-02 12:36:31

Initialize the return value once and use a single exit path in
find_primary_domain_index().

This is a small cleanup that keeps the existing behavior unchanged while
making the control flow easier to follow.

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v1:
- Handle comments from Christophe Leroy

 arch/powerpc/mm/numa.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index f4cf3ae036de..c44a80d8fc11 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -432,7 +432,7 @@ static void __init initialize_form2_numa_distance_lookup_table(void)
 
 static int __init find_primary_domain_index(void)
 {
-	int index;
+	int index = -1;
 	struct device_node *root;
 
 	/*

@@ -502,12 +502,9 @@ static int __init find_primary_domain_index(void)
 		distance_ref_points_depth = MAX_DISTANCE_REF_POINTS;
 	}
 
-	of_node_put(root);
-	return index;
-
 err:
 	of_node_put(root);
-	return -1;
+	return index;
 }
 
 static void __init get_n_mem_cells(int *n_addr_cells, int *n_size_cells)

-- 
2.43.7

[PATCH v3 3/3] powerpc/numa: Support coregroup on PowerNV

From: Srikar Dronamraju <hidden>
Date: 2026-09-02 12:36:41

Coregroup support on powerpc has so far been limited to PowerVM LPARs.
However, PowerNV can also support coregroups when firmware exposes the
required coregroup information through the associativity hierarchy.

Detect coregroup support by checking whether primary_domain_index is the
penultimate domain in the CPU node's ibm,associativity property. On
PowerNV, a non-penultimate primary_domain_index indicates that firmware
provides an additional level for coregroup information.

This keeps the logic compatible with PowerVM systems, where
primary_domain_index is likewise not the penultimate associativity
domain.

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v2:
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
  patch 3 to build correctly)

Changelog from v1: https://lkml.kernel.org/r/20260524010017.140408-1-srikar@linux.ibm.com
- Handle comments from Christophe Leroy; make code more flat

 arch/powerpc/mm/numa.c | 58 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 48 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 5f326b005a2a..e97b624203ea 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -889,12 +889,32 @@ static int __init numa_setup_drmem_lmb(struct drmem_lmb *lmb,
 	return 0;
 }
 
+/*
+ * If hierarchy extends beyond primary_domain_index + 1, then next
+ * level corresponds to coregroup.
+ */
+static int detect_and_enable_coregroup(const __be32 *associativity, int index)
+{
+	if (!associativity || index == -1)
+		goto out;
+
+	index = of_read_number(associativity, 1);
+
+	if (index > primary_domain_index + 1) {
+		coregroup_enabled = 1;
+		return index;
+	}
+out:
+	coregroup_enabled = 0;
+	return -1;
+}
+
 static int __init parse_numa_properties(void)
 {
 	struct device_node *memory, *pci;
-	int default_nid = 0;
-	unsigned long i;
+	int default_nid = 0, index = 0;
 	const __be32 *associativity;
+	unsigned long i;
 
 	if (numa_enabled == 0) {
 		pr_warn("disabled by user\n");

@@ -927,7 +947,6 @@ static int __init parse_numa_properties(void)
 	 */
 	for_each_present_cpu(i) {
 		__be32 vphn_assoc[VPHN_ASSOC_BUFSIZE];
-		struct device_node *cpu;
 		int nid = NUMA_NO_NODE;
 
 		memset(vphn_assoc, 0, VPHN_ASSOC_BUFSIZE * sizeof(__be32));

@@ -935,7 +954,9 @@ static int __init parse_numa_properties(void)
 		if (__vphn_get_associativity(i, vphn_assoc) == 0) {
 			nid = associativity_to_nid(vphn_assoc);
 			initialize_form1_numa_distance(vphn_assoc);
+			index = detect_and_enable_coregroup(vphn_assoc, index);
 		} else {
+			struct device_node *cpu;
 
 			/*
 			 * Don't fall back to default_nid yet -- we will plug

@@ -948,6 +969,7 @@ static int __init parse_numa_properties(void)
 			associativity = of_get_associativity(cpu);
 			if (associativity) {
 				nid = associativity_to_nid(associativity);
+				index = detect_and_enable_coregroup(associativity, index);
 				initialize_form1_numa_distance(associativity);
 			}
 			of_node_put(cpu);

@@ -1445,7 +1467,9 @@ static long vphn_get_associativity(unsigned long cpu,
 
 int cpu_to_coregroup_id(int cpu)
 {
-	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
+	int coregroup_id = cpu_to_core_id(cpu);
+	struct device_node *cpunode = NULL;
+	const __be32 *associativity;
 	int index;
 
 	if (cpu < 0 || cpu > nr_cpu_ids)

@@ -1454,17 +1478,31 @@ int cpu_to_coregroup_id(int cpu)
 	if (!coregroup_enabled)
 		goto out;
 
-	if (!firmware_has_feature(FW_FEATURE_VPHN))
-		goto out;
+	if (firmware_has_feature(FW_FEATURE_VPHN)) {
+		__be32 tmp[VPHN_ASSOC_BUFSIZE] = {0};
 
-	if (vphn_get_associativity(cpu, associativity))
+		if (vphn_get_associativity(cpu, tmp))
+			goto out;
+
+		associativity = tmp;
+
+	} else {
+		cpunode = of_get_cpu_node(cpu, NULL);
+		if (!cpunode)
+			goto out;
+
+		associativity = of_get_associativity(cpunode);
+	}
+	if (!associativity)
 		goto out;
 
 	index = of_read_number(associativity, 1);
 	if (index > primary_domain_index + 1)
-		return of_read_number(&associativity[index - 1], 1);
+		coregroup_id = of_read_number(&associativity[index - 1], 1);
 
 out:
-	return cpu_to_core_id(cpu);
-}
+	if (cpunode)
+		of_node_put(cpunode);
 
+	return coregroup_id;
+}

-- 
2.43.7

[PATCH v3 2/3] powerpc/numa: Allow cpu_to_coregroup_id without PPC_SPLPAR

From: Srikar Dronamraju <hidden>
Date: 2026-09-02 12:36:50

Make cpu_to_coregroup_id() available outside PPC_SPLPAR so it can be
used by platforms that do not rely on the SPLPAR-specific VPHN path.

Keep the existing fallback behavior by returning the core ID when
coregroup information is unavailable.

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v2:
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
  patch 3 to build correctly)

Changelog from v1:
- Handle comments from Christophe Leroy; Remove extern key word in
  declaration

 arch/powerpc/include/asm/topology.h | 15 +++++++--------
 arch/powerpc/mm/numa.c              | 22 +++++++++++++++-------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 44ec416fa489..02c3c9ab3ea9 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h

@@ -71,6 +71,7 @@ extern void map_cpu_to_node(int cpu, int node);
 extern void unmap_cpu_from_node(unsigned long cpu);
 #endif /* CONFIG_HOTPLUG_CPU */
 
+int cpu_to_coregroup_id(int cpu);
 #else
 
 static inline int early_cpu_to_node(int cpu) { return 0; }

@@ -107,14 +108,6 @@ static inline void map_cpu_to_node(int cpu, int node) {}
 static inline void unmap_cpu_from_node(unsigned long cpu) {}
 #endif /* CONFIG_HOTPLUG_CPU */
 #endif /* CONFIG_SMP */
-
-#endif /* CONFIG_NUMA */
-
-#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
-void find_and_update_cpu_nid(int cpu);
-extern int cpu_to_coregroup_id(int cpu);
-#else
-static inline void find_and_update_cpu_nid(int cpu) {}
 static inline int cpu_to_coregroup_id(int cpu)
 {
 #ifdef CONFIG_SMP

@@ -124,6 +117,12 @@ static inline int cpu_to_coregroup_id(int cpu)
 #endif
 }
 
+#endif /* CONFIG_NUMA */
+
+#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
+void find_and_update_cpu_nid(int cpu);
+#else
+static inline void find_and_update_cpu_nid(int cpu) {}
 #endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
 
 #include <asm-generic/topology.h>

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index c44a80d8fc11..5f326b005a2a 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -1428,6 +1428,21 @@ void find_and_update_cpu_nid(int cpu)
 	pr_debug("%s:%d cpu %d nid %d\n", __func__, __LINE__, cpu, new_nid);
 }
 
+static int topology_update_init(void)
+{
+	topology_inited = 1;
+	return 0;
+}
+device_initcall(topology_update_init);
+
+#else
+static long vphn_get_associativity(unsigned long cpu,
+					__be32 *associativity)
+{
+	return -1;
+}
+#endif /* CONFIG_PPC_SPLPAR */
+
 int cpu_to_coregroup_id(int cpu)
 {
 	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};

@@ -1453,10 +1468,3 @@ int cpu_to_coregroup_id(int cpu)
 	return cpu_to_core_id(cpu);
 }
 
-static int topology_update_init(void)
-{
-	topology_inited = 1;
-	return 0;
-}
-device_initcall(topology_update_init);
-#endif /* CONFIG_PPC_SPLPAR */

-- 
2.43.7

Re: [PATCH v3 2/3] powerpc/numa: Allow cpu_to_coregroup_id without PPC_SPLPAR

From: Shrikanth Hegde <sshegde@linux.ibm.com>
Date: 2026-09-04 09:59:33


On 9/2/26 6:05 PM, Srikar Dronamraju wrote:

quoted hunk

Make cpu_to_coregroup_id() available outside PPC_SPLPAR so it can be
used by platforms that do not rely on the SPLPAR-specific VPHN path.

Keep the existing fallback behavior by returning the core ID when
coregroup information is unavailable.

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v2:
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
   patch 3 to build correctly)

Changelog from v1:
- Handle comments from Christophe Leroy; Remove extern key word in
   declaration

  arch/powerpc/include/asm/topology.h | 15 +++++++--------
  arch/powerpc/mm/numa.c              | 22 +++++++++++++++-------
  2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 44ec416fa489..02c3c9ab3ea9 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h

@@ -71,6 +71,7 @@ extern void map_cpu_to_node(int cpu, int node);
  extern void unmap_cpu_from_node(unsigned long cpu);
  #endif /* CONFIG_HOTPLUG_CPU */
  
+int cpu_to_coregroup_id(int cpu);

nit:

I prefer extern before declaration so that i can see it is defined
elsewhere.

Other than that, rest looks good to me.

Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>

quoted hunk

  #else
  
  static inline int early_cpu_to_node(int cpu) { return 0; }

@@ -107,14 +108,6 @@ static inline void map_cpu_to_node(int cpu, int node) {}
  static inline void unmap_cpu_from_node(unsigned long cpu) {}
  #endif /* CONFIG_HOTPLUG_CPU */
  #endif /* CONFIG_SMP */
-
-#endif /* CONFIG_NUMA */
-
-#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
-void find_and_update_cpu_nid(int cpu);
-extern int cpu_to_coregroup_id(int cpu);
-#else
-static inline void find_and_update_cpu_nid(int cpu) {}
  static inline int cpu_to_coregroup_id(int cpu)
  {
  #ifdef CONFIG_SMP

@@ -124,6 +117,12 @@ static inline int cpu_to_coregroup_id(int cpu)
  #endif
  }
  
+#endif /* CONFIG_NUMA */
+
+#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
+void find_and_update_cpu_nid(int cpu);
+#else
+static inline void find_and_update_cpu_nid(int cpu) {}
  #endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
  
  #include <asm-generic/topology.h>

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index c44a80d8fc11..5f326b005a2a 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -1428,6 +1428,21 @@ void find_and_update_cpu_nid(int cpu)
  	pr_debug("%s:%d cpu %d nid %d\n", __func__, __LINE__, cpu, new_nid);
  }
  
+static int topology_update_init(void)
+{
+	topology_inited = 1;
+	return 0;
+}
+device_initcall(topology_update_init);
+
+#else
+static long vphn_get_associativity(unsigned long cpu,
+					__be32 *associativity)
+{
+	return -1;
+}
+#endif /* CONFIG_PPC_SPLPAR */
+
  int cpu_to_coregroup_id(int cpu)
  {
  	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};

@@ -1453,10 +1468,3 @@ int cpu_to_coregroup_id(int cpu)
  	return cpu_to_core_id(cpu);
  }
  
-static int topology_update_init(void)
-{
-	topology_inited = 1;
-	return 0;
-}
-device_initcall(topology_update_init);
-#endif /* CONFIG_PPC_SPLPAR */

Re: [PATCH v3 3/3] powerpc/numa: Support coregroup on PowerNV

From: Shrikanth Hegde <sshegde@linux.ibm.com>
Date: 2026-09-04 10:05:22


On 9/2/26 6:05 PM, Srikar Dronamraju wrote:

Coregroup support on powerpc has so far been limited to PowerVM LPARs.
However, PowerNV can also support coregroups when firmware exposes the
required coregroup information through the associativity hierarchy.

Existing firmware does expose this info already?

Detect coregroup support by checking whether primary_domain_index is the
penultimate domain in the CPU node's ibm,associativity property. On
PowerNV, a non-penultimate primary_domain_index indicates that firmware
provides an additional level for coregroup information.

This keeps the logic compatible with PowerVM systems, where
primary_domain_index is likewise not the penultimate associativity
domain.

Could you please put the ibm,associativity on this powernv? as well
PowerVM's so that one understands it better?

quoted hunk

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v2:
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
   patch 3 to build correctly)

Changelog from v1: https://lkml.kernel.org/r/20260524010017.140408-1-srikar@linux.ibm.com
- Handle comments from Christophe Leroy; make code more flat

  arch/powerpc/mm/numa.c | 58 ++++++++++++++++++++++++++++++++++--------
  1 file changed, 48 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 5f326b005a2a..e97b624203ea 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -889,12 +889,32 @@ static int __init numa_setup_drmem_lmb(struct drmem_lmb *lmb,
  	return 0;
  }
  
+/*
+ * If hierarchy extends beyond primary_domain_index + 1, then next
+ * level corresponds to coregroup.
+ */
+static int detect_and_enable_coregroup(const __be32 *associativity, int index)
+{
+	if (!associativity || index == -1)
+		goto out;
+
+	index = of_read_number(associativity, 1);
+
+	if (index > primary_domain_index + 1) {
+		coregroup_enabled = 1;
+		return index;
+	}
+out:
+	coregroup_enabled = 0;
+	return -1;
+}
+
  static int __init parse_numa_properties(void)
  {
  	struct device_node *memory, *pci;
-	int default_nid = 0;
-	unsigned long i;
+	int default_nid = 0, index = 0;
  	const __be32 *associativity;
+	unsigned long i;
  
  	if (numa_enabled == 0) {
  		pr_warn("disabled by user\n");

@@ -927,7 +947,6 @@ static int __init parse_numa_properties(void)
  	 */
  	for_each_present_cpu(i) {
  		__be32 vphn_assoc[VPHN_ASSOC_BUFSIZE];
-		struct device_node *cpu;
  		int nid = NUMA_NO_NODE;
  
  		memset(vphn_assoc, 0, VPHN_ASSOC_BUFSIZE * sizeof(__be32));

@@ -935,7 +954,9 @@ static int __init parse_numa_properties(void)
  		if (__vphn_get_associativity(i, vphn_assoc) == 0) {
  			nid = associativity_to_nid(vphn_assoc);
  			initialize_form1_numa_distance(vphn_assoc);
+			index = detect_and_enable_coregroup(vphn_assoc, index);

nit: I don't see return value being used.

Other than that, rest looks good to me.
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>

quoted hunk

  		} else {
+			struct device_node *cpu;
  
  			/*
  			 * Don't fall back to default_nid yet -- we will plug

@@ -948,6 +969,7 @@ static int __init parse_numa_properties(void)
  			associativity = of_get_associativity(cpu);
  			if (associativity) {
  				nid = associativity_to_nid(associativity);
+				index = detect_and_enable_coregroup(associativity, index);
  				initialize_form1_numa_distance(associativity);
  			}
  			of_node_put(cpu);
@@ -1445,7 +1467,9 @@ static long vphn_get_associativity(unsigned long cpu,
  
  int cpu_to_coregroup_id(int cpu)
  {
-	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
+	int coregroup_id = cpu_to_core_id(cpu);
+	struct device_node *cpunode = NULL;
+	const __be32 *associativity;
  	int index;
  
  	if (cpu < 0 || cpu > nr_cpu_ids)
@@ -1454,17 +1478,31 @@ int cpu_to_coregroup_id(int cpu)
  	if (!coregroup_enabled)
  		goto out;
  
-	if (!firmware_has_feature(FW_FEATURE_VPHN))
-		goto out;
+	if (firmware_has_feature(FW_FEATURE_VPHN)) {
+		__be32 tmp[VPHN_ASSOC_BUFSIZE] = {0};
  
-	if (vphn_get_associativity(cpu, associativity))
+		if (vphn_get_associativity(cpu, tmp))
+			goto out;
+
+		associativity = tmp;
+
+	} else {
+		cpunode = of_get_cpu_node(cpu, NULL);
+		if (!cpunode)
+			goto out;
+
+		associativity = of_get_associativity(cpunode);
+	}
+	if (!associativity)
  		goto out;
  
  	index = of_read_number(associativity, 1);
  	if (index > primary_domain_index + 1)
-		return of_read_number(&associativity[index - 1], 1);
+		coregroup_id = of_read_number(&associativity[index - 1], 1);
  
  out:
-	return cpu_to_core_id(cpu);
-}
+	if (cpunode)
+		of_node_put(cpunode);
  
+	return coregroup_id;
+}

Re: [PATCH v3 1/3] powerpc/numa: Simplify find_primary_domain_index

From: Shrikanth Hegde <sshegde@linux.ibm.com>
Date: 2026-09-04 10:06:13


On 9/2/26 6:05 PM, Srikar Dronamraju wrote:

Initialize the return value once and use a single exit path in
find_primary_domain_index().

This is a small cleanup that keeps the existing behavior unchanged while
making the control flow easier to follow.

Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>

quoted hunk

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v1:
- Handle comments from Christophe Leroy

  arch/powerpc/mm/numa.c | 7 ++-----
  1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index f4cf3ae036de..c44a80d8fc11 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -432,7 +432,7 @@ static void __init initialize_form2_numa_distance_lookup_table(void)
  
  static int __init find_primary_domain_index(void)
  {
-	int index;
+	int index = -1;
  	struct device_node *root;
  
  	/*

@@ -502,12 +502,9 @@ static int __init find_primary_domain_index(void)
  		distance_ref_points_depth = MAX_DISTANCE_REF_POINTS;
  	}
  
-	of_node_put(root);
-	return index;
-
  err:
  	of_node_put(root);
-	return -1;
+	return index;
  }
  
  static void __init get_n_mem_cells(int *n_addr_cells, int *n_size_cells)

Re: [PATCH v3 2/3] powerpc/numa: Allow cpu_to_coregroup_id without PPC_SPLPAR

From: Srikar Dronamraju <hidden>
Date: 2026-09-04 11:11:13

* Shrikanth Hegde [off-list ref] [2026-09-04 15:29:03]:


On 9/2/26 6:05 PM, Srikar Dronamraju wrote:

quoted

Make cpu_to_coregroup_id() available outside PPC_SPLPAR so it can be
used by platforms that do not rely on the SPLPAR-specific VPHN path.

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 44ec416fa489..02c3c9ab3ea9 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h

@@ -71,6 +71,7 @@ extern void map_cpu_to_node(int cpu, int node);
  extern void unmap_cpu_from_node(unsigned long cpu);
  #endif /* CONFIG_HOTPLUG_CPU */
+int cpu_to_coregroup_id(int cpu);

nit:

I prefer extern before declaration so that i can see it is defined
elsewhere.

Hey Shrikanth,

Thanks for taking a look.

It was done on intention based on comment from Christophe Leroy here
https://lkml.kernel.org/r/6387fb12-76f1-4503-8ac2-3ca777c0186e@kernel.org

Other than that, rest looks good to me.

Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju

Re: [PATCH v3 3/3] powerpc/numa: Support coregroup on PowerNV

From: Srikar Dronamraju <hidden>
Date: 2026-09-04 11:34:49

* Shrikanth Hegde [off-list ref] [2026-09-04 15:34:50]:

Thanks Shrikanth for taking a look.


On 9/2/26 6:05 PM, Srikar Dronamraju wrote:

quoted

Coregroup support on powerpc has so far been limited to PowerVM LPARs.
However, PowerNV can also support coregroups when firmware exposes the
required coregroup information through the associativity hierarchy.

Existing firmware does expose this info already?

The corresponding skiboot changes were sent to the skiboot mailing list.

quoted

Detect coregroup support by checking whether primary_domain_index is the
penultimate domain in the CPU node's ibm,associativity property. On
PowerNV, a non-penultimate primary_domain_index indicates that firmware
provides an additional level for coregroup information.

This keeps the logic compatible with PowerVM systems, where
primary_domain_index is likewise not the penultimate associativity
domain.

Could you please put the ibm,associativity on this powernv? as well
PowerVM's so that one understands it better?

With this patch and the skiboot change, the ibm,associativity will look
similar.

For example on a Power10 Baremetal box with skiboot changes.

$ lsprop /proc/device-tree/cpus/PowerPC,POWER10@*/ibm,associativity |& head -n 20
PowerPC,POWER10@0/ibm,associativity
		 00000005 00000000 00000000 00000000 00000000 00000000
PowerPC,POWER10@100/ibm,associativity
		 00000005 00000000 00000001 00000001 00000002 00000000
PowerPC,POWER10@108/ibm,associativity
		 00000005 00000000 00000001 00000001 00000002 00000002
PowerPC,POWER10@10/ibm,associativity
		 00000005 00000000 00000000 00000000 00000001 00000004
PowerPC,POWER10@110/ibm,associativity
		 00000005 00000000 00000001 00000001 00000003 00000004
PowerPC,POWER10@118/ibm,associativity
		 00000005 00000000 00000001 00000001 00000003 00000006
PowerPC,POWER10@120/ibm,associativity
		 00000005 00000000 00000001 00000001 00000002 00000008
PowerPC,POWER10@128/ibm,associativity
		 00000005 00000000 00000001 00000001 00000002 0000000a
PowerPC,POWER10@130/ibm,associativity
		 00000005 00000000 00000001 00000001 00000003 0000000c
PowerPC,POWER10@138/ibm,associativity
		 00000005 00000000 00000001 00000001 00000003 0000000e

quoted

Signed-off-by: Srikar Dronamraju <redacted>
---
Changelog from v2:
- Handle comments from Ritesh (one hunk needed to be moved from patch 2 to
   patch 3 to build correctly)

Changelog from v1: https://lkml.kernel.org/r/20260524010017.140408-1-srikar@linux.ibm.com
- Handle comments from Christophe Leroy; make code more flat

  arch/powerpc/mm/numa.c | 58 ++++++++++++++++++++++++++++++++++--------
  1 file changed, 48 insertions(+), 10 deletions(-)

-- 
Thanks and Regards
Srikar Dronamraju

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