[PATCH v7 07/12] sched/debug: Add migration stats due to non preferred CPUs

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Add a new stat,
- nr_migrations_cpu_non_preferred: number of migrations happened since
  a CPU was marked as non preferred due to high steal time.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
v6->v7:
- Check if rq indeed changed or not before increment.

 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 10 ++++++++--
 kernel/sched/debug.c  |  1 +
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 968b18a7f470..37849d2f1dbd 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 74c93a88bf84..1ca1eefbdaf9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11324,8 +11324,14 @@ static int sched_non_preferred_cpu_push_stop(void *arg)
 
 	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;
+
+		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);
 	raw_spin_unlock_irq(&p->pi_lock);
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 72236db67983..5ebb2055e6d5 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1446,6 +1446,7 @@ 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);
-- 
2.47.3