Re: [PATCH] pc: q35: Bump max_cpus to 512

[Daniel P . Berrangé]

On Mon, May 09, 2022 at 09:12:49AM +0200, Igor Mammedov wrote:
> On Wed, 4 May 2022 08:16:39 -0500
> Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> wrote:
> 
> > This is the maximum number of vCPU supported by
> > the AMD x2APIC virtualization.
> > 
> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> > ---
> >  hw/i386/pc_q35.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > index 302288342a..e82b1c690d 100644
> > --- a/hw/i386/pc_q35.c
> > +++ b/hw/i386/pc_q35.c
> > @@ -357,7 +357,7 @@ static void pc_q35_machine_options(MachineClass *m)
> >      machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
> >      machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);
> >      machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
> > -    m->max_cpus = 288;
> > +    m->max_cpus = 512;
> 
> Maybe we should bump it to KVM VCPU maximum,
> and make sure we error out if asked for combination of
> hardware/irqchip is not usable.

In RHEL downstream we currently bump this to 710 CPUs, because you
overflow the SMBIOS 2.1 tables at approx 720 CPUs (give/take a little
depending on other config options).

Going beyond 710 CPUs value requires using the SMBIOS 3 entry point.

AFAIK, the x86 machine types still default to SMBIOS 2.1, so that
would need changing too.

With regards,
Daniel
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