[PATCH v10 03/13] lib/group_cpus: Add group_mask_cpus_evenly()

Aaron Tomlin
2026-04-02T14:14:47Z

From: Daniel Wagner <wagi@kernel.org>

group_mask_cpu_evenly() allows the caller to pass in a CPU mask that
should be evenly distributed. This new function is a more generic
version of the existing group_cpus_evenly(), which always distributes
all present CPUs into groups.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
include/linux/group_cpus.h | 3 ++
lib/group_cpus.c | 59 ++++++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+)

diff --git a/include/linux/group_cpus.h b/include/linux/group_cpus.h
index 9d4e5ab6c314..defab4123a82 100644
--- a/include/linux/group_cpus.h
+++ b/include/linux/group_cpus.h
@@ -10,5 +10,8 @@
#include <linux/cpu.h>

struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks);
+struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
+ const struct cpumask *mask,
+ unsigned int *nummasks);

#endif
diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index b8d54398f88a..d3e9a20250ff 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -8,6 +8,7 @@
#include <linux/cpu.h>
#include <linux/sort.h>
#include <linux/group_cpus.h>
+#include <linux/sched/isolation.h>

static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
unsigned int cpus_per_grp)
@@ -563,3 +564,61 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
return masks;
}
EXPORT_SYMBOL_GPL(group_cpus_evenly);
+
+/**
+ * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
+ * @numgrps: number of cpumasks to create
+ * @mask: CPUs to consider for the grouping
+ * @nummasks: number of initialized cpusmasks
+ *
+ * Return: cpumask array if successful, NULL otherwise. Only the CPUs
+ * marked in the mask will be considered for the grouping. And each
+ * element includes CPUs assigned to this group. nummasks contains the
+ * number of initialized masks which can be less than numgrps. cpu_mask
+ *
+ * Try to put close CPUs from viewpoint of CPU and NUMA locality into
+ * same group, and run two-stage grouping:
+ * 1) allocate present CPUs on these groups evenly first
+ * 2) allocate other possible CPUs on these groups evenly
+ *
+ * We guarantee in the resulted grouping that all CPUs are covered, and
+ * no same CPU is assigned to multiple groups
+ */
+struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
+ const struct cpumask *mask,
+ unsigned int *nummasks)
+{
+ cpumask_var_t *node_to_cpumask;
+ cpumask_var_t nmsk;
+ int ret = -ENOMEM;
+ struct cpumask *masks = NULL;
+
+ if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
+ return NULL;
+
+ node_to_cpumask = alloc_node_to_cpumask();
+ if (!node_to_cpumask)
+ goto fail_nmsk;
+
+ masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
+ if (!masks)
+ goto fail_node_to_cpumask;
+
+ build_node_to_cpumask(node_to_cpumask);
+
+ ret = __group_cpus_evenly(0, numgrps, node_to_cpumask, mask, nmsk,
+ masks);
+
+fail_node_to_cpumask:
+ free_node_to_cpumask(node_to_cpumask);
+
+fail_nmsk:
+ free_cpumask_var(nmsk);
+ if (ret < 0) {
+ kfree(masks);
+ return NULL;
+ }
+ *nummasks = ret;
+ return masks;
+}
+EXPORT_SYMBOL_GPL(group_mask_cpus_evenly);
--
2.51.0