linux-kernel - [tip: sched/core] sched: Don't account irq time if sched_clock

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Message-ID: <173693263425.31546.8534211192244236490.tip-bot2@tip-bot2>
Date: Wed, 15 Jan 2025 09:17:14 -0000
From: "tip-bot2 for Yafang Shao" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Yafang Shao <laoar.shao@...il.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, mkoutny@...e.com,
 Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Don't account irq time if
 sched_clock_irqtime is disabled

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     763a744e24a8cfbcc13f699dcdae13a627b8588e
Gitweb:        https://git.kernel.org/tip/763a744e24a8cfbcc13f699dcdae13a627b8588e
Author:        Yafang Shao <laoar.shao@...il.com>
AuthorDate:    Fri, 03 Jan 2025 10:24:07 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 13 Jan 2025 14:10:25 +01:00

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@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Michal Koutný <mkoutny@...e.com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lore.kernel.org/r/20250103022409.2544-3-laoar.shao@gmail.com
---
 kernel/sched/core.c | 44 +++++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8490293..22dfcd3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -740,29 +740,31 @@ 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))) {