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Re: [Xen-merge] Re: [patch] SMP alternatives for i386

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-merge] Re: [patch] SMP alternatives for i386
From: Zwane Mwaikambo <zwane@xxxxxxxxxxxxxxxx>
Date: Wed, 14 Dec 2005 17:20:19 -0800 (PST)
Cc: Gerd Knorr <kraxel@xxxxxxx>, Xen merge mainline list <xen-merge@xxxxxxxxxxxxxxxxxxx>, linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
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Hello Keir,

On Wed, 14 Dec 2005, Keir Fraser wrote:

> >     fixup_irqs(map);
> >     /* It's now safe to remove this processor from the online map */
> >     cpu_clear(cpu, cpu_online_map);
> > +
> > +   if (1 == num_online_cpus())
> > +           alternatives_smp_switch(0);
> >     return 0;
> >  }
> > 
> > Is that really safe there? Ideally you want to do the switch when the
> > processor going offline is no longer executing kernel code.
> 
> Perhaps that check belongs at the end of __cpu_die()? That's where it lives in
> xen's smpboot.c.

Yes indeed, end of __cpu_die would be perfect for x86 too as that's where 
CPU_DEAD acknowledge is checked.


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