Re: [PATCH -tip/core/rcu 3/6] Simplify RCU CPU-hotplug notification

Lai Jiangshan
2009-08-20T04:02:27Z

Paul E. McKenney wrote:
> From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> Use the new cpu_notifier() API to simplify RCU's CPU-hotplug
> notifiers, collapsing down to a single such notifier. This
> makes it trivial to provide the notifier-ordering guarantee
> that rcu_barrier() depends on. Also remove redundant
> open_softirq() calls from Hierarchical RCU notifier.
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> kernel/rcupdate.c | 16 +++++++++++++++-
> kernel/rcupreempt.c | 25 ++-----------------------
> kernel/rcutree.c | 17 +++++------------
> 3 files changed, 22 insertions(+), 36 deletions(-)
>
> diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
> index eae29c2..8df1156 100644
> --- a/kernel/rcupdate.c
> +++ b/kernel/rcupdate.c
> @@ -217,9 +217,13 @@ static void rcu_migrate_callback(struct rcu_head *notused)
> wake_up(&rcu_migrate_wq);
> }
>
> +extern int rcu_cpu_notify(struct notifier_block *self,
> + unsigned long action, void *hcpu);
> +
> static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
> unsigned long action, void *hcpu)
> {
> + rcu_cpu_notify(self, action, hcpu);
> if (action == CPU_DYING) {
> /*
> * preempt_disable() in on_each_cpu() prevents stop_machine(),
> @@ -244,8 +248,18 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
>
> void __init rcu_init(void)
> {
> + int i;
> +
> __rcu_init();
> - hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
> + cpu_notifier(rcu_barrier_cpu_hotplug, 0);
> +
> + /*
> + * We don't need protection against CPU-hotplug here because
> + * this is called early in boot, before either interrupts
> + * or the scheduler are operational.
> + */
> + for_each_online_cpu(i)
> + rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);

I think,
There is only one cpu in cpu online map at early boot time,
it is the current cpu.

Thanks, Lai