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

To: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCHEs]: support more than 32 VCPUs in guests
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 26 Jul 2010 17:37:37 -0700
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 On 07/26/2010 03:57 PM, Jeremy Fitzhardinge wrote:
 On 06/15/2010 11:45 AM, Mukesh Rathor wrote:
On Tue, 15 Jun 2010 09:30:35 +0100
Jeremy Fitzhardinge<jeremy@xxxxxxxx>  wrote:

On 06/15/2010 03:49 AM, Mukesh Rathor wrote:
On Mon, 14 Jun 2010 10:37:30 +0100
Jeremy Fitzhardinge<jeremy@xxxxxxxx>  wrote:


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

Ok, attached  patch without BUG_ON. Please feel free to modify
to your liking also.

It looks like you smashed all the tabs into spaces so its hard to see
what you've changed in the diff.  I'll fix it up and give it a
look-over.

     J
Sorry, I've tabs turned off because patches I submit to other product I
work on must be tab free.  Anyways, re attached a new one with tabs.

This doesn't compile with CONFIG_SMP=n because setup_max_cpus doesn't exist. For now I've just put a couple of #ifdef CONFIG_SMPs in there to avoid compile errors, but could you look at coming up with a cleaner solution?

Hm, I committed a tidier version.  I don't see it getting much better.

    J

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