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timers: Fix nextevt calculation when no timers are pending

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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: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-13-anna-maria@linutronix.de
This commit is contained in:
Anna-Maria Behnsen 2023-12-01 10:26:34 +01:00 committed by Thomas Gleixner
parent bb8caad508
commit da65f29dad
1 changed files with 11 additions and 2 deletions
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13
kernel/time/timer.c
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@ -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;
}
/*