[PATCH v7 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>
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
---
 kernel/sched/psi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 84dad1511d1e..893d454c82ae 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -998,7 +998,7 @@ void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_st
 	s64 delta;
 	u64 irq;
 
-	if (static_branch_likely(&psi_disabled))
+	if (static_branch_likely(&psi_disabled) || !irqtime_enabled())
 		return;
 
 	if (!curr->pid)
@@ -1240,6 +1240,9 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 	if (static_branch_likely(&psi_disabled))
 		return -EOPNOTSUPP;
 
+	if (!irqtime_enabled() && res == PSI_IRQ)
+		return -EOPNOTSUPP;
+
 	/* Update averages before reporting them */
 	mutex_lock(&group->avgs_lock);
 	now = sched_clock();
-- 
2.43.5