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

Anna-Maria Behnsen
2022-10-25T13:59:44Z

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@linutronix.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