Commit 0e81fe79 authored by Shrikanth Hegde's avatar Shrikanth Hegde Committed by Peter Zijlstra
Browse files

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: default avatarShrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Link: https://patch.msgid.link/20260323193630.640311-3-sshegde@linux.ibm.com
parent 76504bce

kernel/sched/core.c

+4 −2
Original line number Diff line number Diff line
@@ -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;



	/*