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? > 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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