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

JIRA: https://issues.redhat.com/browse/RHEL-78821

commit 763a744
Author: Yafang Shao <laoar.shao@gmail.com>
Date:   Fri Jan 3 10:24:07 2025 +0800

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

    sched_clock_irqtime may be disabled due to the clock source, in which case
    IRQ time should not be accounted. Let's add a conditional check to avoid
    unnecessary logic.

    Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Michal Koutný <mkoutny@suse.com>
    Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
    Link: https://lore.kernel.org/r/20250103022409.2544-3-laoar.shao@gmail.com

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

kernel/sched/core.c

@@ -701,29 +701,31 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 	s64 __maybe_unused steal = 0, irq_delta = 0;
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
-	irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
+	if (irqtime_enabled()) {
+		irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
 
-	/*
-	 * Since irq_time is only updated on {soft,}irq_exit, we might run into
-	 * this case when a previous update_rq_clock() happened inside a
-	 * {soft,}IRQ region.
-	 *
-	 * When this happens, we stop ->clock_task and only update the
-	 * prev_irq_time stamp to account for the part that fit, so that a next
-	 * update will consume the rest. This ensures ->clock_task is
-	 * monotonic.
-	 *
-	 * It does however cause some slight miss-attribution of {soft,}IRQ
-	 * time, a more accurate solution would be to update the irq_time using
-	 * the current rq->clock timestamp, except that would require using
-	 * atomic ops.
-	 */
-	if (irq_delta > delta)
-		irq_delta = delta;
+		/*
+		 * Since irq_time is only updated on {soft,}irq_exit, we might run into
+		 * this case when a previous update_rq_clock() happened inside a
+		 * {soft,}IRQ region.
+		 *
+		 * When this happens, we stop ->clock_task and only update the
+		 * prev_irq_time stamp to account for the part that fit, so that a next
+		 * update will consume the rest. This ensures ->clock_task is
+		 * monotonic.
+		 *
+		 * It does however cause some slight miss-attribution of {soft,}IRQ
+		 * time, a more accurate solution would be to update the irq_time using
+		 * the current rq->clock timestamp, except that would require using
+		 * atomic ops.
+		 */
+		if (irq_delta > delta)
+			irq_delta = delta;
 
-	rq->prev_irq_time += irq_delta;
-	delta -= irq_delta;
-	delayacct_irq(rq->curr, irq_delta);
+		rq->prev_irq_time += irq_delta;
+		delta -= irq_delta;
+		delayacct_irq(rq->curr, irq_delta);
+	}
 #endif
 #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
 	if (static_key_false((&paravirt_steal_rq_enabled))) {