linux-kernel - [tip: timers/core] timers: Introduce add_timer() variants which modify timer flags

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Date: Thu, 22 Feb 2024 17:12:14 -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: Introduce add_timer() variants which
 modify timer flags

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

Commit-ID:     8e7e247f64a1e0fee430aba28d9108f7598eb237
Gitweb:        https://git.kernel.org/tip/8e7e247f64a1e0fee430aba28d9108f7598eb237
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Wed, 21 Feb 2024 10:05:33 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 22 Feb 2024 17:52:30 +01:00

timers: Introduce add_timer() variants which modify timer flags

A timer might be used as a pinned timer (using add_timer_on()) and later on
as non-pinned timer using add_timer(). When the "NOHZ timer pull at expiry
model" is in place, the TIMER_PINNED flag is required to be used whenever a
timer needs to expire on a dedicated CPU. Otherwise the flag must not be
set if expiration on a dedicated CPU is not required.

add_timer_on()'s behavior will be changed during the preparation patches
for the "NOHZ timer pull at expiry model" to unconditionally set the
TIMER_PINNED flag. To be able to clear/ set the flag when queueing a
timer, two variants of add_timer() are introduced.

This is a preparatory step and has 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/20240221090548.36600-6-anna-maria@linutronix.de

---
 include/linux/timer.h |  2 ++
 kernel/time/timer.c   | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index f18a2f1..2be8be6 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -165,6 +165,8 @@ extern int timer_reduce(struct timer_list *timer, unsigned long expires);
 #define NEXT_TIMER_MAX_DELTA	((1UL << 30) - 1)
 
 extern void add_timer(struct timer_list *timer);
+extern void add_timer_local(struct timer_list *timer);
+extern void add_timer_global(struct timer_list *timer);
 
 extern int try_to_del_timer_sync(struct timer_list *timer);
 extern int timer_delete_sync(struct timer_list *timer);
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 74cfe21..bef8cb8 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1291,6 +1291,40 @@ void add_timer(struct timer_list *timer)
 EXPORT_SYMBOL(add_timer);
 
 /**
+ * add_timer_local() - Start a timer on the local CPU
+ * @timer:	The timer to be started
+ *
+ * Same as add_timer() except that the timer flag TIMER_PINNED is set.
+ *
+ * See add_timer() for further details.
+ */
+void add_timer_local(struct timer_list *timer)
+{
+	if (WARN_ON_ONCE(timer_pending(timer)))
+		return;
+	timer->flags |= TIMER_PINNED;
+	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
+}
+EXPORT_SYMBOL(add_timer_local);
+
+/**
+ * add_timer_global() - Start a timer without TIMER_PINNED flag set
+ * @timer:	The timer to be started
+ *
+ * Same as add_timer() except that the timer flag TIMER_PINNED is unset.
+ *
+ * See add_timer() for further details.
+ */
+void add_timer_global(struct timer_list *timer)
+{
+	if (WARN_ON_ONCE(timer_pending(timer)))
+		return;
+	timer->flags &= ~TIMER_PINNED;
+	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
+}
+EXPORT_SYMBOL(add_timer_global);
+
+/**
  * add_timer_on - Start a timer on a particular CPU
  * @timer:	The timer to be started
  * @cpu:	The CPU to start it on