[Xen-devel] Re: [PATCHEs]: support more than 32 VCPUs in guests

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 06/10/2010 03:13 AM, Mukesh Rathor wrote:
> Well, BUG_ON is only triggered if booting more than 32 VCPUs on a *very
> old* xen (pre xen 3.1.0). 
>
> Looking at code closely, we could just set setup_max_cpus to 32 some
> where in xen function, perhaps even in xen_vcpu_setup(). That way
> later in smp_init() it would just be ok. 
>   

Yes.

> One thing tho, the per cpus areas are already setup at that point, so that 
> would need to be cleaned. BTW, I don't understand why 
> have_vcpu_info_placement is set to 0 in xen_guest_init()? 
>   

xen_guest_init is used by the pvhvm path, and hvm domains don't have a
notion of vcpu info placement.

> What minimum version of xen is required to run pvops kernel?
>   

In theory it should be back-compatible for all Xen 3, but in practice it
tweaks lots of bugs in older Xens (particularly 32-on-64).  I don't know
that anyone has definitively established an earliest version.  I
implemented vcpu info placement for use in pvops kernels, but it was
never my intention that it be an absolute requirement.

    J

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