On Fri, Sep 10, 2010 at 05:46:34PM +0200, Peter Zijlstra wrote: > On Fri, 2010-09-10 at 08:37 -0700, Paul E. McKenney wrote: > > > So, you say below that it works because synchronize_srcu(), that > > > waits for qs after touching pmus, implies synchronize_sched(), right? > > > > Ook... My current plans to fold SRCU into TREE_RCU would invalidate > > this assumption. > > > > Maybe we need some sort of primitive that concurrently waits for > > multiple types of RCU grace periods? > > Nah, but I was thinking that any kind of preemptible rcu sync would > imply a sched rcu sync. Ah! Although disabling interrupts will block preemptible RCU grace periods in current implementations (but please don't rely on this!), disabling preemption will -not- block preemptible RCU grace periods, even given current TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations. Current SRCU grace periods are blocked by disabling preemption, but folding it into the tree/tiny implementations would make SRCU grace periods be no longer blocked by disabling preemption. This might change if RCU priority boosting is enabled, due to RCU grace-period computation and callback invocation moving to a kthread, but I won't have the guts to make TREE_RCU use kthread by default for some time. (Probably a year or so trouble-free experience with RCU priority boosting/kthreads.) > If not strictly implied I'd have no problem simply writing: > > synchronize_rcu_sched(); > synchronize_srcu(); If that works for you, then we are set! The only reason to introduce a combined primitive would be if the latency of the above was too large. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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