Re: [Xen-devel] [PATCH] x86: correct socket_cpumask allocation for AP

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2015-07-09 at 09:58 +0800, Chao Peng wrote:
> On Wed, Jul 08, 2015 at 05:32:11PM +0100, Jan Beulich wrote:
> > >>> On 08.07.15 at 18:17, <dario.faggioli@xxxxxxxxxx> wrote:
> > > I think it has to do with the fact that I've got CPU #0 on socket #1,
> > > while Boris' (and perhaps Chao's too) test box have it on socket #0.
> > 
> > Ah, yes, this is indeed a case I didn't consider when validating
> > Chao's analysis.
> 
> I apologize, this is what I have made the wrong assumption on
> from the beginning.
>
Yes, it's quite easy to get caught by this, I've been in similar
situation too (i.e., with code working in completely different ways
depending on whether CPU#0 was on socket 0 or not). :-)

> While looks the fix is simple, just change
> 'zalloc_cpumask_var(socket_cpumask)' to
> 'zalloc_cpumask_var(socket_cpumask + cpu_to_socket(0))'
> for booting cpu in smp_prepare_cpus().
> 
FWIW, I can confirm that doing this (on top of the already submitted
patch) makes the issue go away on my hardware.

I can't verify whether things are working properly, though, as I don't
have any CAT enabled system handy.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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