Messages in this thread | | | Subject | Re: [RFC PATCH 06/15] nohz_task: Keep the tick if rcu needs it | From | Peter Zijlstra <> | Date | Mon, 20 Dec 2010 16:58:20 +0100 |
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On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> @@ -1634,7 +1633,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) > * by the current CPU, returning 1 if so. This function is part of the > * RCU implementation; it is -not- an exported member of the RCU API. > */ > -static int rcu_pending(int cpu) > +int rcu_pending(int cpu)
/me wonders about that comment.
> { > return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) || > __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) || > diff --git a/kernel/sched.c b/kernel/sched.c > index 6dbae46..45bd6e2 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2470,10 +2470,16 @@ static void nohz_task_cpu_update(void *unused) > int nohz_task_can_stop_tick(void) > { > struct rq *rq = this_rq(); > + int cpu; > > if (rq->nr_running > 1) > return 0; > > + cpu = smp_processor_id(); > + > + if (rcu_pending(cpu) || rcu_needs_cpu(cpu)) > + return 0;
Arguable, rcu_needs_cpu() should imply rcu_pending(), because if there's work still to be done, it needs the cpu, hmm?
> return 1; > } >
This patch also implies you broke stuff with #4 because it would put the machine to sleep while RCU still had bits to do, not very nice.
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