On Wed, 24 Apr 2013 06:18:50 -0500 Robin Holt <h...@sgi.com> wrote:
> We recently noticed that reboot of a 1024 cpu machine takes approx 16
> minutes of just stopping the cpus. The slowdown was tracked to commit
> f96972f.
>
> The current implementation does all the work of hot removing the cpus
> before halting the system. We are switching to just migrating to the
> boot cpu and then continuing with shutdown/reboot.
>
> This also has the effect of not breaking x86's command line parameter for
> specifying the reboot cpu. Note, this code was shamelessly copied from
> arch/x86/kernel/reboot.c with bits removed pertaining to the reboot_cpu
> command line parameter.
>
> @@ -357,6 +357,24 @@ int unregister_reboot_notifier(struct notifier_block *nb)
> }
> EXPORT_SYMBOL(unregister_reboot_notifier);
>
> +static void migrate_to_reboot_cpu(void)
> +{
> + /* The boot cpu is always logical cpu 0 */
> + int reboot_cpu_id = 0;
> +
> + cpu_hotplug_disable();
> +
> + /* Make certain the cpu I'm about to reboot on is online */
> + if (!cpu_online(reboot_cpu_id))
> + reboot_cpu_id = cpumask_first(cpu_online_mask);
> +
> + /* Prevent races with other tasks migrating this task */
> + current->flags |= PF_THREAD_BOUND;
PF_THREAD_BOUND was removed/replaced in linux-next's a9ab775bc
("workqueue: directly restore CPU affinity of workers from CPU_ONLINE")
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