Messages in this thread Patch in this message | | | Date | Thu, 16 Aug 2012 14:55:11 -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 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.
Thanx, Paul
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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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