Messages in this thread | | | Date | Mon, 15 Aug 2011 10:04:17 -0400 | From | Josh Boyer <> | Subject | Re: 3.0-git15 Atomic scheduling in pidmap_init |
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On Sun, Aug 14, 2011 at 04:04:53PM -0700, Paul E. McKenney wrote: > > > > > Now rcu_init_percpu_data() still sets rdp->qs_pending to 1, and that > > > > > is going to stay as is as long as preemption is disabled. > > > > > > > > But setting rdp->qs_pending to 1 in rcu_init_percpu_data() has no effect > > > > until a grace period starts. So, if grace periods are prevented from > > > > Er... really? Because it gets set and __rcu_pending looks at it > > unconditionally in the case that is calling set_need_resched. It > > doesn't check if there is anything about a grace period going on or not. > > Frederic noted the condition that prevents this at boot time, but it > appears that newly onlined CPUs might send themselves needless resched > IPIs at runtime if RCU is idle. > > > > > starting, no need to mess with rcu_init_percpu_data(). Especially given > > > > that rcu_init_percpu_data() is also used at late boot and runtime for > > > > CPU hotplug. > > > > > > Ok. > > > > > > > > > > > So I believe that it is sufficient to change cpu_needs_another_gp() > > > > to check for boot being far enough along to allow grace periods. > > > > > > Yep, sounds good. > > > > I looked at doing this but got lost as to 1) how it would help the > > situtation I've reported, and 2) exactly how to do that. > > It would prevent control from reaching that point, and that might > well be needed for other reasons. (This bit about RCU needing to > work differently at boot time is, well, "interesting".) > > > I'd be happy to test, but at the moment the proposed solution is > > confusing to me. > > Please see the attached.
Fixed it up quickly to apply on top of -rc2 and it seems to solve the problem nicely. Thanks for the patch.
josh
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