Messages in this thread | | | Date | Mon, 9 Jul 2018 10:53:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested |
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On Fri, Jul 06, 2018 at 10:11:50AM -0700, Paul E. McKenney wrote: > On Fri, Jul 06, 2018 at 06:29:05PM +0200, Peter Zijlstra wrote: > > On Fri, Jul 06, 2018 at 03:53:30PM +0100, David Woodhouse wrote: > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > > index e4d4e60..89f5814 100644 > > > --- a/include/linux/sched.h > > > +++ b/include/linux/sched.h > > > @@ -1616,7 +1616,8 @@ static inline int spin_needbreak(spinlock_t *lock) > > > > > > static __always_inline bool need_resched(void) > > > { > > > - return unlikely(tif_need_resched()); > > > + return unlikely(tif_need_resched()) || > > > + rcu_urgent_qs_requested(); > > > } > > > > Instead of making need_resched() touch two cachelines, I think I would > > prefer adding resched_cpu() to rcu_request_urgent_qs_task(). > > I used to do something like this, but decided that whacking each holdout > CPU over the head ten times a second was a bit much.
This is only called from the !list_empty(rcu_tasks_holdout) loop in rcu_tasks_kthread afaict, and that has a schedule_timeout_interruptible(HZ) in it, which I read as once a second.
Which seems like an entirely reasonable amount of time to kick a task. Not scheduling for a second is like an eternity.
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