sched/core: Get this cpu once in ttwu_queue_cond()

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 could add up to a small value.

ttwu_queue_cond is called with interrupt disabled. So preemption is
disabled. Hence cache the value once instead.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Link: https://patch.msgid.link/20260323193630.640311-3-sshegde@linux.ibm.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 64b467c1d5b6e328e473556abb6cdbe88aa99aa7..7c7d4bf686d71e10b960677f4dc37ee2932d7284 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3842,6 +3842,8 @@ bool cpus_share_resources(int this_cpu, int that_cpu)
 
 static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
 {
+       int this_cpu = smp_processor_id();
+
        /* See SCX_OPS_ALLOW_QUEUED_WAKEUP. */
        if (!scx_allow_ttwu_queue(p))
                return false;
@@ -3866,10 +3868,10 @@ static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
         * If the CPU does not share cache, then queue the task on the
         * remote rqs wakelist to avoid accessing remote data.
         */
-       if (!cpus_share_cache(smp_processor_id(), cpu))
+       if (!cpus_share_cache(this_cpu, cpu))
                return true;
 
-       if (cpu == smp_processor_id())
+       if (cpu == this_cpu)
                return false;
 
        /*