[tip: sched/core] sched/fair: Get this cpu once in find_new_ilb()
From: tip-bot2 for Shrikanth Hegde
Date: Tue Mar 24 2026 - 05:19:34 EST
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 76504bce4ee6b8757647e07bc1710dcac9acdc2e
Gitweb: https://git.kernel.org/tip/76504bce4ee6b8757647e07bc1710dcac9acdc2e
Author: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
AuthorDate: Tue, 24 Mar 2026 01:06:27 +05:30
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 24 Mar 2026 10:07:04 +01:00
sched/fair: Get this cpu once in find_new_ilb()
Calling smp_processor_id() on:
- In CONFIG_DEBUG_PREEMPT=y, if preemption/irq is disabled, then it does
not print any warning.
- In CONFIG_DEBUG_PREEMPT=n, it doesn't do anything apart from getting
__smp_processor_id
So with both CONFIG_DEBUG_PREEMPT=y/n, in preemption disabled section
it is better to cache the value. It could save a few cycles. Though
tiny, repeated in loop could add up to a small value.
find_new_ilb is called in interrupt context. So preemption is disabled.
So Hoist the this_cpu out of loop
Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@xxxxxxxxx>
Reviewed-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Link: https://patch.msgid.link/20260323193630.640311-2-sshegde@xxxxxxxxxxxxx
---
kernel/sched/fair.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0a35a82..2265092 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12614,14 +12614,14 @@ static inline int on_null_domain(struct rq *rq)
*/
static inline int find_new_ilb(void)
{
+ int this_cpu = smp_processor_id();
const struct cpumask *hk_mask;
int ilb_cpu;
hk_mask = housekeeping_cpumask(HK_TYPE_KERNEL_NOISE);
for_each_cpu_and(ilb_cpu, nohz.idle_cpus_mask, hk_mask) {
-
- if (ilb_cpu == smp_processor_id())
+ if (ilb_cpu == this_cpu)
continue;
if (idle_cpu(ilb_cpu))