hrtimer: Avoid re-evaluation when nothing changed

Most times there is no change between hrtimer_interrupt() deferring the rearm
and the invocation of hrtimer_rearm_deferred(). In those cases it's a pointless
exercise to re-evaluate the next expiring timer.

Cache the required data and use it if nothing changed.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163431.338569372@kernel.org

1 files changed, 27 insertions, 26 deletions

diff --git a/include/linux/hrtimer_defs.h b/include/linux/hrtimer_defs.h
index 2c3bdbd562d2..b6846efec210 100644
--- a/include/linux/hrtimer_defs.h
+++ b/include/linux/hrtimer_defs.h
@@ -47,32 +47,31 @@ enum  hrtimer_base_type {
 
 /**
  * struct hrtimer_cpu_base - the per cpu clock bases
- * @lock:		lock protecting the base and associated clock bases
- *			and timers
- * @cpu:		cpu number
- * @active_bases:	Bitfield to mark bases with active timers
- * @clock_was_set_seq:	Sequence counter of clock was set events
- * @hres_active:	State of high resolution mode
- * @deferred_rearm:	A deferred rearm is pending
- * @hang_detected:	The last hrtimer interrupt detected a hang
- * @softirq_activated:	displays, if the softirq is raised - update of softirq
- *			related settings is not required then.
- * @nr_events:		Total number of hrtimer interrupt events
- * @nr_retries:		Total number of hrtimer interrupt retries
- * @nr_hangs:		Total number of hrtimer interrupt hangs
- * @max_hang_time:	Maximum time spent in hrtimer_interrupt
- * @softirq_expiry_lock: Lock which is taken while softirq based hrtimer are
- *			 expired
- * @online:		CPU is online from an hrtimers point of view
- * @timer_waiters:	A hrtimer_cancel() invocation waits for the timer
- *			callback to finish.
- * @expires_next:	absolute time of the next event, is required for remote
- *			hrtimer enqueue; it is the total first expiry time (hard
- *			and soft hrtimer are taken into account)
- * @next_timer:		Pointer to the first expiring timer
- * @softirq_expires_next: Time to check, if soft queues needs also to be expired
- * @softirq_next_timer: Pointer to the first expiring softirq based timer
- * @clock_base:		array of clock bases for this cpu
+ * @lock:			lock protecting the base and associated clock bases and timers
+ * @cpu:			cpu number
+ * @active_bases:		Bitfield to mark bases with active timers
+ * @clock_was_set_seq:		Sequence counter of clock was set events
+ * @hres_active:		State of high resolution mode
+ * @deferred_rearm:		A deferred rearm is pending
+ * @deferred_needs_update:	The deferred rearm must re-evaluate the first timer
+ * @hang_detected:		The last hrtimer interrupt detected a hang
+ * @softirq_activated:		displays, if the softirq is raised - update of softirq
+ *				related settings is not required then.
+ * @nr_events:			Total number of hrtimer interrupt events
+ * @nr_retries:			Total number of hrtimer interrupt retries
+ * @nr_hangs:			Total number of hrtimer interrupt hangs
+ * @max_hang_time:		Maximum time spent in hrtimer_interrupt
+ * @softirq_expiry_lock:	Lock which is taken while softirq based hrtimer are expired
+ * @online:			CPU is online from an hrtimers point of view
+ * @timer_waiters:		A hrtimer_cancel() waiters for the timer callback to finish.
+ * @expires_next:		Absolute time of the next event, is required for remote
+ *				hrtimer enqueue; it is the total first expiry time (hard
+ *				and soft hrtimer are taken into account)
+ * @next_timer:			Pointer to the first expiring timer
+ * @softirq_expires_next:	Time to check, if soft queues needs also to be expired
+ * @softirq_next_timer:		Pointer to the first expiring softirq based timer
+ * @deferred_expires_next:	Cached expires next value for deferred rearm
+ * @clock_base:			Array of clock bases for this cpu
  *
  * Note: next_timer is just an optimization for __remove_hrtimer().
  *	 Do not dereference the pointer because it is not reliable on
@@ -85,6 +84,7 @@ struct hrtimer_cpu_base {
 	unsigned int			clock_was_set_seq;
 	bool				hres_active;
 	bool				deferred_rearm;
+	bool				deferred_needs_update;
 	bool				hang_detected;
 	bool				softirq_activated;
 	bool				online;
@@ -102,6 +102,7 @@ struct hrtimer_cpu_base {
 	struct hrtimer			*next_timer;
 	ktime_t				softirq_expires_next;
 	struct hrtimer			*softirq_next_timer;
+	ktime_t				deferred_expires_next;
 	struct hrtimer_clock_base	clock_base[HRTIMER_MAX_CLOCK_BASES];
 	call_single_data_t		csd;
 } ____cacheline_aligned;