Messages in this thread | | | Date | Mon, 13 Oct 2008 20:03:31 +0200 | From | Manfred Spraul <> | Subject | Re: [PATCH, RFC] v7 scalable classic RCU implementation |
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Paul E. McKenney wrote: > Do you send a reschedule IPI to CPUs that are not in dyntick idle mode, > but who have failed to pass through a quiescent state? > Actually, I never send reschedule IPIs.
- For "usual" cpus, rcu_check_callbacks() checks for quiescent states. There should be a set_need_resched() if a cpu holds up a grace period for too long. I just haven't implemented it yet. IMHO it doesn't make sense to perform a "for_each_cpu() smd_send_reschedule()". rcu has a hook in each cpu, thus a set_need_resched() by the per-cpu hook is faster/simpler.
- For nohz cpus, a poller function [schedule_work(), enabled interrupts] peeks into the per-cpu data of the nohz cpu and checks if it is quiet or if it passed through a quiescent state. If it didn't, then it sets a cpu_data->kick_poller flag and rcu_irq_exit() reports the grace period. No need for an IPI either - rcu has a hook in the irq exit path.
Right now, I cheat if a nohz cpu is in a long-running nmi [while(other_cpu_is_in_nmi()) cpu_relax()], but I think I can fix that with an set_need_resched() in the rcu_nmi_exit().
-- Manfred
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