[PATCH v5 12/18] timer: Add get next timer interrupt functionality for remote CPUs

Anna-Maria Behnsen
2023-03-01T14:19:08Z

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 | 8 +++++++
kernel/time/timer.c | 46 +++++++++++++++++++++++++++++++++----
2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 649f2b48e8f0..28471c8f8c9c 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -8,6 +8,11 @@
#include "timekeeping.h"
#include "tick-sched.h"

+struct timer_events {
+ u64 local;
+ u64 global;
+};
+
#ifdef CONFIG_GENERIC_CLOCKEVENTS

# define TICK_DO_TIMER_NONE -1
@@ -164,6 +169,9 @@ static inline void timers_update_nohz(void) { }
DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);

extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem);
+extern void fetch_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 dfc744545159..9daaef5d2f6f 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -221,11 +221,6 @@ struct timer_base {

static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);

-struct timer_events {
- u64 local;
- u64 global;
-};
-
#ifdef CONFIG_NO_HZ_COMMON

static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
@@ -1984,6 +1979,47 @@ static unsigned long fetch_next_timer_interrupt(struct timer_base *base_local,
return local_first ? nextevt_local : nextevt_global;
}

+/**
+ * fetch_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 fetch_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);
+
+ fetch_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 base clock is done only when @basej is past base->clk, otherwise
* base-clk might be rewind.
--
2.30.2