Commit da65f29d authored by Anna-Maria Behnsen's avatar Anna-Maria Behnsen Committed by Thomas Gleixner
Browse files

timers: Fix nextevt calculation when no timers are pending 



When no timer is queued into an empty timer base, the next_expiry will not
be updated. It was originally calculated as

  base->clk + NEXT_TIMER_MAX_DELTA

When the timer base stays empty long enough (> NEXT_TIMER_MAX_DELTA), the
next_expiry value of the empty base suggests that there is a timer pending
soon. This might be more a kind of a theoretical problem, but the fix
doesn't hurt.

Use only base->next_expiry value as nextevt when timers are
pending. Otherwise nextevt will be jiffies + NEXT_TIMER_MAX_DELTA. As all
information is in place, update base->next_expiry value of the empty timer
base as well.

Signed-off-by: default avatarAnna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-13-anna-maria@linutronix.de
parent bb8caad5

kernel/time/timer.c

+11 −2
Original line number Diff line number Diff line
@@ -1922,8 +1922,8 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) 
u64 get_next_timer_interrupt(unsigned long basej, u64 basem)

{

	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);

	unsigned long nextevt = basej + NEXT_TIMER_MAX_DELTA;

	u64 expires = KTIME_MAX;

	unsigned long nextevt;

	bool was_idle;



	/*
@@ -1936,7 +1936,6 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) 
	raw_spin_lock(&base->lock);

	if (base->next_expiry_recalc)

		next_expiry_recalc(base);

	nextevt = base->next_expiry;



	/*

	 * We have a fresh next event. Check whether we can forward the
@@ -1945,10 +1944,20 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) 
	__forward_timer_base(base, basej);



	if (base->timers_pending) {

		nextevt = base->next_expiry;



		/* If we missed a tick already, force 0 delta */

		if (time_before(nextevt, basej))

			nextevt = basej;

		expires = basem + (u64)(nextevt - basej) * TICK_NSEC;

	} else {

		/*

		 * Move next_expiry for the empty base into the future to

		 * prevent a unnecessary raise of the timer softirq when the

		 * next_expiry value will be reached even if there is no timer

		 * pending.

		 */

		base->next_expiry = nextevt;

	}



	/*