[PATCH 2/2] sched: Add a check for cpu unbound deferrable timers

[Prasad Sodagudi <psodagud@codeaurora.org>]

Add a check for cpu unbound deferrable timer expiry and raise
softirq for handling the expired timers so that the CPU can
process the cpu unbound deferrable times as early as possible
when a cpu tries to enter/exit idle loop.

Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
---
 include/linux/timer.h    |  3 +++
 kernel/time/tick-sched.c |  6 ++++++
 kernel/time/timer.c      | 29 ++++++++++++++++++++++++++++-
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 1e6650e..25a1837 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -172,6 +172,9 @@ extern int del_timer(struct timer_list * timer);
 extern int mod_timer(struct timer_list *timer, unsigned long expires);
 extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
 extern int timer_reduce(struct timer_list *timer, unsigned long expires);
+#ifdef CONFIG_SMP
+extern bool check_pending_deferrable_timers(int cpu);
+#endif
 
 /*
  * The jiffies value which is added to now, when there is no timer
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index a792d21..fe0836a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
+#include <linux/timer.h>
 #include <linux/context_tracking.h>
 #include <linux/mm.h>
 
@@ -948,6 +949,11 @@ static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
 	ktime_t expires;
 	int cpu = smp_processor_id();
 
+#ifdef CONFIG_SMP
+	if (check_pending_deferrable_timers(cpu))
+		raise_softirq_irqoff(TIMER_SOFTIRQ);
+#endif
+
 	/*
 	 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
 	 * tick timer expiration time is known already.
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a63ca77..3b0aac3 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -221,6 +221,7 @@ static DECLARE_WORK(timer_update_work, timer_update_keys);
 
 #ifdef CONFIG_SMP
 struct timer_base timer_base_deferrable;
+static atomic_t deferrable_pending;
 unsigned int sysctl_timer_migration = 1;
 
 DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
@@ -1609,6 +1610,31 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
 	return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
 }
 
+
+#ifdef CONFIG_SMP
+/*
+ * check_pending_deferrable_timers - Check for unbound deferrable timer expiry
+ * @cpu - Current CPU
+ *
+ * The function checks whether any global deferrable pending timers
+ * are exipired or not. This function does not check cpu bounded
+ * diferrable pending timers expiry.
+ *
+ * The function returns true when a cpu unbounded deferrable timer is expired.
+ */
+bool check_pending_deferrable_timers(int cpu)
+{
+	if (cpu == tick_do_timer_cpu ||
+		tick_do_timer_cpu == TICK_DO_TIMER_NONE) {
+		if (time_after_eq(jiffies, timer_base_deferrable.clk)
+			&& !atomic_cmpxchg(&deferrable_pending, 0, 1)) {
+			return true;
+		}
+	}
+	return false;
+}
+#endif
+
 /**
  * get_next_timer_interrupt - return the time (clock mono) of the next timer
  * @basej:	base time jiffies
@@ -1799,7 +1825,8 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 	__run_timers(base);
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) {
 		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
-		if (tick_do_timer_cpu == TICK_DO_TIMER_NONE ||
+		if ((atomic_cmpxchg(&deferrable_pending, 1, 0) &&
+				tick_do_timer_cpu == TICK_DO_TIMER_NONE) ||
 				tick_do_timer_cpu == smp_processor_id())
 			__run_timers(&timer_base_deferrable);
 	}
-- 
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