| From | Anna-Maria Behnsen <> | Subject | [PATCH v9 12/32] timers: Fix nextevt calculation when no timers are pending | Date | Fri, 1 Dec 2023 10:26:34 +0100 |
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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> --- v9: New patch --- kernel/time/timer.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 0826018d9873..4dffe966424c 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -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; /* * Pretend that there is no timer pending if the cpu is offline. @@ -1935,7 +1935,6 @@ 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 @@ -1944,10 +1943,20 @@ 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; } /* -- 2.39.2
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