Messages in this thread | | | Date | Mon, 9 Jul 2018 13:42:48 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested |
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On Mon, Jul 09, 2018 at 09:35:38PM +0100, David Woodhouse wrote: > > > On Mon, 2018-07-09 at 13:34 -0700, Paul E. McKenney wrote: > > > > So here are the possible code paths when .rcu_urgent_qs is set to true: > > > > 1. A context switch will record the quiescent state and clear > > .rcu_urgent_qs. (The failure to do the clearing in current -rcu > > for PREEMPT builds is a performance bug that I need to fix.) > > What if there's nothing else runnable and there is no actual context > switch?
The scheduler invokes rcu_note_context_switch() before looking to see if there really will or won't be a context switch.
I am sure that Peter will correct me if I am confused on this point. ;-)
Thanx, Paul
> > 2. A cond_resched() will cause rcu_all_qs() to be invoked, which > > will record a quiescent state and clear .rcu_urgent_qs. > > > > 3. With the patch below, a scheduling-clock interrupt of a > > non-idle non-userspace task will force a reschedule, which > > will result in #1 above happening.
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