linux-kernel - [tip: timers/core] timers: Clarify check in forward_timer

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Message-ID: <170308794817.398.17855561566614353854.tip-bot2@tip-bot2>
Date: Wed, 20 Dec 2023 15:59:08 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 Thomas Gleixner <tglx@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers: Clarify check in forward_timer_base()

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

Commit-ID:     8a2c9c7e7848d7f63d38b698209148b5bb4ba7f3
Gitweb:        https://git.kernel.org/tip/8a2c9c7e7848d7f63d38b698209148b5bb4ba7f3
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Fri, 01 Dec 2023 10:26:30 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 20 Dec 2023 16:49:38 +01:00

timers: Clarify check in forward_timer_base()

The current check whether a forward of the timer base is required can be
simplified by using an already existing comparison function which is easier
to read. The related comment is outdated and was not updated when the check
changed in commit 36cd28a4cdd0 ("timers: Lower base clock forwarding
threshold").

Use time_before_eq() for the check and replace the comment by copying the
comment from the same check inside get_next_timer_interrupt(). Move the
precious information of the outdated comment to the proper place in
__run_timers().

No functional change.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-9-anna-maria@linutronix.de

---
 kernel/time/timer.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 490ff8e..f75f932 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -944,11 +944,10 @@ static inline void forward_timer_base(struct timer_base *base)
 	unsigned long jnow = READ_ONCE(jiffies);
 
 	/*
-	 * No need to forward if we are close enough below jiffies.
-	 * Also while executing timers, base->clk is 1 offset ahead
-	 * of jiffies to avoid endless requeuing to current jiffies.
+	 * Check whether we can forward the base. We can only do that when
+	 * @basej is past base->clk otherwise we might rewind base->clk.
 	 */
-	if ((long)(jnow - base->clk) < 1)
+	if (time_before_eq(jnow, base->clk))
 		return;
 
 	/*
@@ -2021,6 +2020,10 @@ static inline void __run_timers(struct timer_base *base)
 		 */
 		WARN_ON_ONCE(!levels && !base->next_expiry_recalc
 			     && base->timers_pending);
+		/*
+		 * While executing timers, base->clk is set 1 offset ahead of
+		 * jiffies to avoid endless requeuing to current jiffies.
+		 */
 		base->clk++;
 		next_expiry_recalc(base);