[tip: sched/core] sched/debug: Add migration stats due to non preferred CPUs

[tip-bot2 for Shrikanth Hegde]

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

Commit-ID:     68957caaa9c0e127bc87fee64e45be843f6c5c91
Gitweb:        https://git.kernel.org/tip/68957caaa9c0e127bc87fee64e45be843f6c5c91
Author:        Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
AuthorDate:    Mon, 28 Sep 2026 11:07:24 +05:30
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 28 Sep 2026 08:44:42 +02:00

sched/debug: Add migration stats due to non preferred CPUs

Add a new per-task stat,
- nr_migrations_cpu_non_preferred: number of push migrations while the
  CPU is non-preferred.

Since this new stat is per-task, it changes only /proc/<pid>/sched.
It doesn't update /proc/schedstat. Hence increasing the schedstat version
is not necessary.

Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260928053728.797539-10-sshegde@xxxxxxxxxxxxx
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   |  9 +++++++--
 kernel/sched/debug.c  |  1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d7cc771..48639b0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -554,6 +554,7 @@ struct sched_statistics {
 	u64				nr_failed_migrations_running;
 	u64				nr_failed_migrations_hot;
 	u64				nr_forced_migrations;
+	u64				nr_migrations_cpu_non_preferred;
 
 	u64				nr_wakeups;
 	u64				nr_wakeups_sync;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0e40055..0bb86a4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11288,8 +11288,13 @@ static int sched_non_preferred_cpu_push_stop(void *arg)
 		update_rq_clock(rq);
 		context_unsafe_alias(rq);
 
-		if (task_rq(p) == rq && task_on_rq_queued(p))
-			rq = __migrate_task(rq, &rf, p, cpu);
+		if (task_rq(p) == rq && task_on_rq_queued(p)) {
+			struct rq *dest_rq = __migrate_task(rq, &rf, p, cpu);
+
+			if (rq != dest_rq)
+				schedstat_inc(p->stats.nr_migrations_cpu_non_preferred);
+			rq = dest_rq;
+		}
 		rq_unlock(rq, &rf);
 	}
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index fda10b3..e6a3b51 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1440,6 +1440,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 		P_SCHEDSTAT(nr_failed_migrations_running);
 		P_SCHEDSTAT(nr_failed_migrations_hot);
 		P_SCHEDSTAT(nr_forced_migrations);
+		P_SCHEDSTAT(nr_migrations_cpu_non_preferred);
 		P_SCHEDSTAT(nr_wakeups);
 		P_SCHEDSTAT(nr_wakeups_sync);
 		P_SCHEDSTAT(nr_wakeups_migrate);