[PATCH 6.18 040/175] sched/fair: Have SD_SERIALIZE affect newidle balancing

Greg Kroah-Hartman
2026-02-09T14:27:19Z

From: Peter Zijlstra <peterz@infradead.org>

commit 522fb20fbdbe48ed98f587d628637ff38ececd2d upstream.

Also serialize the possiblty much more frequent newidle balancing for
the 'expensive' domains that have SD_BALANCE set.

Initial benchmarking by K Prateek and Tim showed no negative effect.

Split out from the larger patch moving sched_balance_running around
for ease of bisect and such.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Seconded-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/df068896-82f9-458d-8fff-5a2f654e8ffd@amd.com
Link: https://patch.msgid.link/6fed119b723c71552943bfe5798c93851b30a361.1762800251.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/sched/fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11744,7 +11744,7 @@ redo:
goto out_balanced;
}

- if (!need_unlock && (sd->flags & SD_SERIALIZE) && idle != CPU_NEWLY_IDLE) {
+ if (!need_unlock && (sd->flags & SD_SERIALIZE)) {
int zero = 0;
if (!atomic_try_cmpxchg_acquire(&sched_balance_running, &zero, 1))
goto out_balanced;