The following commit has been merged into the sched/core branch of tip:

Commit-ID:     815c5cb76a3e5dad4fc3911b9073591dc3a29282
Gitweb:        https://git.kernel.org/tip/815c5cb76a3e5dad4fc3911b9073591dc3a29282
Author:        Shrikanth Hegde <sshegde@linux.ibm.com>
AuthorDate:    Fri, 15 May 2026 22:54:53 +05:30
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 19 May 2026 12:17:36 +02:00

topology: Introduce cpu_smt_mask for CONFIG_SCHED_SMT=n

Define cpu_smt_mask in case of CONFIG_SCHED_SMT=n as cpumask_of that
CPU. With that config, it is expected that kernel treats each CPU
as individual core. Using cpumask_of(cpu) reflects that.

This would help to get rid of the ifdeffery that is spread across
the codebase since cpu_smt_mask is defined only in case of
CONFIG_SCHED_SMT=y.

Note: There is no arch today which defines cpu_smt_mask unconditionally.
So likely defining the cpu_smt_mask shouldn't lead redefinition errors.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260515172456.542799-2-sshegde@linux.ibm.com
---
 include/linux/topology.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index 6575af3..709a2dc 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -230,11 +230,24 @@ static inline int cpu_to_mem(int cpu)
 #define topology_drawer_cpumask(cpu)		cpumask_of(cpu)
 #endif
 
-#if defined(CONFIG_SCHED_SMT) && !defined(cpu_smt_mask)
+/*
+ * Defining cpu_smt_mask as cpumask_of that CPU helps to get
+ * rid of lot of ifdeffery all around the codebase in case of
+ * CONFIG_SCHED_SMT=n. It just means there are no other siblings, which
+ * is what is expected.
+ */
+#if defined(CONFIG_SCHED_SMT)
+# if !defined(cpu_smt_mask)
 static inline const struct cpumask *cpu_smt_mask(int cpu)
 {
 	return topology_sibling_cpumask(cpu);
 }
+# endif
+#else	/* !CONFIG_SCHED_SMT */
+static inline const struct cpumask *cpu_smt_mask(int cpu)
+{
+	return cpumask_of(cpu);
+}
 #endif
 
 #ifndef topology_is_primary_thread