linux-kernel - Re: [PATCH -v6 2/5] Migrate shutdown/reboot to boot cpu.

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Message-Id: <20130424151749.30b0680dc9392b110537bcd5@linux-foundation.org>
Date:	Wed, 24 Apr 2013 15:17:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Robin Holt <holt@....com>
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Russ Anderson <rja@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH -v6 2/5] Migrate shutdown/reboot to boot cpu.

On Wed, 24 Apr 2013 06:18:50 -0500 Robin Holt <holt@....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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