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Re: [Xen-devel] [PATCH] Enlarge default NR_CPUS to 64 for x86_64

To: "Wei, Gang" <gang.wei@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Enlarge default NR_CPUS to 64 for x86_64
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 07 Aug 2009 17:18:23 +0100
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On 07/08/2009 15:59, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:

> Not sure about whether we can raise it for i386 too. I am a little confused by
> below lines in config.h:
>     #ifdef __i386__
>     #if NR_CPUS > 32
>     #error "Maximum of 32 physical processors supported by Xen on x86_32"
>     #endif
>     /* Maximum number of virtual CPUs in multi-processor guests. */
>     #endif
> I don't know why this compiling time error was put here for i386 yet. Any body
> know it?

I think it's a hangover from when there was a cpumask_t inside struct
page_info. That structure had to be fixed size for i386 to fit in the
hypervisor's virtual memory footprint.

 -- Keir

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