Messages in this thread | | | Date | Tue, 8 Dec 2020 07:04:46 -0800 | From | "Paul E. McKenney" <> | Subject | Re: timers: Move clearing of base::timer_running under base::lock |
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On Tue, Dec 08, 2020 at 09:50:49AM +0100, Sebastian Andrzej Siewior wrote: > On 2020-12-07 08:06:48 [-0800], Paul E. McKenney wrote: > > > Yes, but it triggers frequently. Like `rcuc' is somehow is aligned with > > > the timeout. > > > > Given that a lot of RCU processing is event-driven based on timers, > > and given that the scheduling-clock interrupts are synchronized for > > energy-efficiency reasons on many configs, maybe this alignment is > > expected behavior? > > No, it is the fact that rcu_preempt has a higher priority than > ksoftirqd. So immediately after the wakeup (of rcu_preempt) there is a > context switch and expire_timers() has this: > > | raw_spin_unlock_irq(&base->lock); > | call_timer_fn(timer, fn, baseclk); > | raw_spin_lock_irq(&base->lock); > | base->running_timer = NULL; > | timer_sync_wait_running(base); > > So ->running_timer isn't reset and try_to_del_timer_sync() (that > del_timer_sync() from schedule_timeout()) returns -1 and then the corner > case is handled where `expiry_lock' is acquired. So everything goes as > expected.
Makes sense! Thank you for the explanation!
Thanx, Paul
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