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SubjectRe: [PATCH -rt 4/5] rcu: backport RCU cpu hotplug support
On Tue, Jun 10, 2008 at 01:13:03PM +0200, Peter Zijlstra wrote:
> backport the RCU cpu-hotplug support from .26-rc to .24-rt

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> kernel/rcupreempt.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 55 insertions(+), 3 deletions(-)
>
> Index: linux-2.6.24.7.noarch/kernel/rcupreempt.c
> ===================================================================
> --- linux-2.6.24.7.noarch.orig/kernel/rcupreempt.c
> +++ linux-2.6.24.7.noarch/kernel/rcupreempt.c
> @@ -820,6 +820,13 @@ void rcu_offline_cpu_rt(int cpu)
> smp_mb(); /* Subsequent RCU read-side critical sections */
> /* seen -after- acknowledgement. */
> }
> +
> + __get_cpu_var(rcu_flipctr)[0] += per_cpu(rcu_flipctr, cpu)[0];
> + __get_cpu_var(rcu_flipctr)[1] += per_cpu(rcu_flipctr, cpu)[1];
> +
> + per_cpu(rcu_flipctr, cpu)[0] = 0;
> + per_cpu(rcu_flipctr, cpu)[1] = 0;
> +
> cpu_clear(cpu, rcu_cpu_online_map);
> spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, oldirq);
>
> @@ -833,8 +840,9 @@ void rcu_offline_cpu_rt(int cpu)
> * fix.
> */
>
> + local_irq_save(oldirq);
> rdp = RCU_DATA_ME();
> - spin_lock_irqsave(&rdp->lock, oldirq);
> + spin_lock(&rdp->lock);
> *rdp->nexttail = list;
> if (list)
> rdp->nexttail = tail;
> @@ -866,9 +874,11 @@ void rcu_process_callbacks_rt(struct sof
> {
> unsigned long flags;
> struct rcu_head *next, *list;
> - struct rcu_data *rdp = RCU_DATA_ME();
> + struct rcu_data *rdp;
>
> - spin_lock_irqsave(&rdp->lock, flags);
> + local_irq_save(flags);
> + rdp = RCU_DATA_ME();
> + spin_lock(&rdp->lock);
> list = rdp->donelist;
> if (list == NULL) {
> spin_unlock_irqrestore(&rdp->lock, flags);
> @@ -951,6 +961,32 @@ int rcu_pending_rt(int cpu)
> return 0;
> }
>
> +static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
> + unsigned long action, void *hcpu)
> +{
> + long cpu = (long)hcpu;
> +
> + switch (action) {
> + case CPU_UP_PREPARE:
> + case CPU_UP_PREPARE_FROZEN:
> + rcu_online_cpu_rt(cpu);
> + break;
> + case CPU_UP_CANCELED:
> + case CPU_UP_CANCELED_FROZEN:
> + case CPU_DEAD:
> + case CPU_DEAD_FROZEN:
> + rcu_offline_cpu_rt(cpu);
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block __cpuinitdata rcu_nb = {
> + .notifier_call = rcu_cpu_notify,
> +};
> +
> void __init rcu_init_rt(void)
> {
> int cpu;
> @@ -972,6 +1008,22 @@ void __init rcu_init_rt(void)
> rdp->donetail = &rdp->donelist;
> }
> rcu_preempt_boost_init();
> + register_cpu_notifier(&rcu_nb);
> +
> + /*
> + * We don't need protection against CPU-Hotplug here
> + * since
> + * a) If a CPU comes online while we are iterating over the
> + * cpu_online_map below, we would only end up making a
> + * duplicate call to rcu_online_cpu() which sets the corresponding
> + * CPU's mask in the rcu_cpu_online_map.
> + *
> + * b) A CPU cannot go offline at this point in time since the user
> + * does not have access to the sysfs interface, nor do we
> + * suspend the system.
> + */
> + for_each_online_cpu(cpu)
> + rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
> }
>
> /*
>
> --
>


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