Messages in this thread | | | Date | Fri, 17 Aug 2012 13:26:48 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC] sched: Make migration_call() safe for stop_machine()-free hotplug |
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On Thu, Aug 16, 2012 at 02:55:11PM -0700, Paul E. McKenney wrote: > On Thu, Aug 16, 2012 at 12:17:10PM -0700, Paul E. McKenney wrote: > > [ . . . ] > > > Another attempted patch below. > > But this time without the brain-dead "using smp_processor_id() in > preemptible" bug.
And the below version passes moderate rcutorture testing.
Thanx, Paul
> ------------------------------------------------------------------------ > > sched: Make migration_call() safe for stop_machine()-free hotplug > > The CPU_DYING branch of migration_call() relies on the fact that > CPU-hotplug offline operations use stop_machine(). This commit therefore > attempts to remedy this situation by moving work to the CPU_DEAD > notifier when the outgoing CPU is quiescent. This requires a small > change to migrate_nr_uninterruptible() to move counts to the current > running CPU instead of a randomly selected CPU. > > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index d325c4b..d09c4e0 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5303,12 +5303,12 @@ void idle_task_exit(void) > * While a dead CPU has no uninterruptible tasks queued at this point, > * it might still have a nonzero ->nr_uninterruptible counter, because > * for performance reasons the counter is not stricly tracking tasks to > - * their home CPUs. So we just add the counter to another CPU's counter, > + * their home CPUs. So we just add the counter to the running CPU's counter, > * to keep the global sum constant after CPU-down: > */ > static void migrate_nr_uninterruptible(struct rq *rq_src) > { > - struct rq *rq_dest = cpu_rq(cpumask_any(cpu_active_mask)); > + struct rq *rq_dest = cpu_rq(smp_processor_id()); > > rq_dest->nr_uninterruptible += rq_src->nr_uninterruptible; > rq_src->nr_uninterruptible = 0; > @@ -5613,9 +5613,19 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) > migrate_tasks(cpu); > BUG_ON(rq->nr_running != 1); /* the migration thread */ > raw_spin_unlock_irqrestore(&rq->lock, flags); > + break; > > - migrate_nr_uninterruptible(rq); > - calc_global_load_remove(rq); > + case CPU_DEAD: > + { > + struct rq *dest_rq = cpu_rq(smp_processor_id()); > + > + local_irq_save(flags); > + raw_spin_lock(&dest_rq->lock); > + migrate_nr_uninterruptible(rq); > + calc_global_load_remove(rq); > + raw_spin_unlock(&dest_rq->lock); > + local_irq_restore(flags); > + } > break; > #endif > }
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