sched, psi: Don't account irq time if sched_clock_irqtime is disabled

JIRA: https://issues.redhat.com/browse/RHEL-78821
Conflicts: Context difference in psi_account_irqtime().

commit a6fd161
Author: Yafang Shao <[email protected]>
Date:   Fri Jan 3 10:24:08 2025 +0800

    sched, psi: Don't account irq time if sched_clock_irqtime is disabled

    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 <[email protected]>
    Signed-off-by: Yafang Shao <[email protected]>
    Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
    Reviewed-by: Michal Koutný <[email protected]>
    Acked-by: Johannes Weiner <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]

Signed-off-by: Phil Auld <[email protected]>

Author: auldp

kernel/sched/psi.c

@@ -999,7 +999,7 @@ 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) || !irqtime_enabled())
 		return;
 
 	if (!curr->pid)
@@ -1241,6 +1241,11 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 	if (static_branch_likely(&psi_disabled))
 		return -EOPNOTSUPP;
 
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+	if (!irqtime_enabled() && res == PSI_IRQ)
+		return -EOPNOTSUPP;
+#endif
+
 	/* Update averages before reporting them */
 	mutex_lock(&group->avgs_lock);
 	now = sched_clock();