linux-kernel - [PATCH v3 10/17] timer: Add get next timer interrupt functionality for remote CPUs

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Date:   Tue, 25 Oct 2022 15:58:43 +0200
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, Arjan van de Ven <arjan@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH v3 10/17] timer: Add get next timer interrupt functionality for remote CPUs

To prepare for the conversion of the NOHZ timer placement to a pull at
expiry time model it's required to have functionality available getting the
next timer interrupt on a remote CPU.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/tick-internal.h |  3 +++
 kernel/time/timer.c         | 41 +++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 6f5f164506d5..7b65abc9d803 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -170,6 +170,9 @@ DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);
 
 extern void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
 					 struct timer_events *tevt);
+extern void get_next_timer_interrupt_remote(unsigned long basej, u64 basem,
+					    struct timer_events *tevt,
+					    unsigned int cpu);
 void timer_clear_idle(void);
 
 #define CLOCK_SET_WALL							\
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 167ae89f0f46..54631e86763f 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1744,6 +1744,47 @@ static unsigned long get_next_timer_interrupt(struct timer_base *base_local,
 	return local_first ? nextevt_local : nextevt_global;
 }
 
+/**
+ * get_next_timer_interrupt_remote
+ * @basej:	base time jiffies
+ * @basem:	base time clock monotonic
+ * @tevt:	Pointer to the storage for the expiry values
+ * @cpu:	Remote CPU
+ *
+ * Stores the next pending local and global timer expiry values in the
+ * struct pointed to by @tevt. If a queue is empty the corresponding
+ * field is set to KTIME_MAX. If local event expires before global
+ * event, global event is set to KTIME_MAX as well.
+ */
+void get_next_timer_interrupt_remote(unsigned long basej, u64 basem,
+				     struct timer_events *tevt,
+				     unsigned int cpu)
+{
+	struct timer_base *base_local, *base_global;
+	unsigned long flags;
+
+	/* Preset local / global events */
+	tevt->local = tevt->global = KTIME_MAX;
+
+	/*
+	 * Pretend that there is no timer pending if the cpu is offline.
+	 * Possible pending timers will be migrated later to an active cpu.
+	 */
+	if (cpu_is_offline(cpu))
+		return;
+
+	base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
+	base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
+
+	raw_spin_lock_irqsave(&base_local->lock, flags);
+	raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
+
+	get_next_timer_interrupt(base_local, base_global, basej, basem, tevt);
+
+	raw_spin_unlock(&base_global->lock);
+	raw_spin_unlock_irqrestore(&base_local->lock, flags);
+}
+
 /**
  * forward_and_idle_timer_bases
  * @basej:	base time jiffies
-- 
2.30.2