[Xen-devel] [PATCH] For running Xen on a 32-way system

["Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>]

Here is a patch to get Xen running on a 32-way Unisys ES7000 system.
Please note that this patch alone is not sufficient to do this. You will
also need the clustered APIC patch that I will be submitting soon. But
since this patch was to a general area in Xen I decided to submit it
separately. I think this patch will be required to get Xen running on
any system that has more than 16 CPUs. 

Here are the following things I did along with the questions I have:

1. I bumped up NR_CPUS to 32 in include/asm-x86/config.h. Is this value
high enough? I know there are some big systems out there. Should this be
bumped up to 64 or 128?

2. Increasing the value of NR_CPUS caused the system to die while
bringing up the 17th CPU. Digging into this I found that the GDT limit
was hard coded for a 16-way. To fix this I had to increase the value of
NR_RESERVED_GDT_ENTRIES in include/public/arch-x86_xx.h. (I am assuming
that NR_RESERVED_GDT_ENTRIES is set by the formula 2*NR_CPUS+8 for
x86_32 and 4*NR_CPUS+8 for x86_64) It seems that there is no correlation
between the two headers, arch-x86_xx.h and config.h. For now I have
explained the correlation with a comment. Should this correlation be
checked somehow at compile time?

3. Should the GDT limit be checked while the system is booting against
the number of CPUs so that the system dies with an appropriate message
rather than just dying while trying to bring up the NR_CPUS+1th CPU?
Will this patch be useful or would it be over kill?

Signed off by Aravindh Puthiyaparambil
<aravindh.puthiyaparambil@xxxxxxxxxx>

Attachment: 32-way.patch
Description: 32-way.patch

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