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

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Date:	Thu, 25 Apr 2013 08:57:04 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Robin Holt <holt@....com>, "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.


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> 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")

I don't see PF_THREAD_BOUND being removed by commit a9ab775bc. Did you 
mean some other commit?

Thanks,

	Ingo
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