[PATCH v3 bpf-next 3/4] sched, psi: Don't account irq time if sched_clock_irqtime is disabled

[Yafang Shao]

sched_clock_irqtime may be disabled due to the clock source. When disabled,
irq_time_read() won't change over time, so there is nothing to account. We
can save iterating the whole hierarchy on every tick and context switch.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 kernel/sched/psi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 020d58967d4e..49d9c75be0c8 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1000,7 +1000,8 @@ void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_st
 	u64 now, irq;
 	s64 delta;
 
-	if (static_branch_likely(&psi_disabled))
+	if (static_branch_likely(&psi_disabled) ||
+	    !static_branch_likely(&sched_clock_irqtime))
 		return;
 
 	if (!curr->pid)
-- 
2.43.5