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

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 9 May 2022 18:41:17 +0700
"Suthikulpanit, Suravee" <suravee.suthikulpanit@amd.com> wrote:

> Igor,
> 
> On 5/9/2022 2:12 PM, 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,  
> 
> Grepping through the Linux kernel source, the KVM_MAX_VCPUS macro is defined per architecture.
> AFAICT, the absolute maximum is for x86, which is 1024. Does that sound about right?

yep

> > and make sure we error out if asked for combination of
> > hardware/irqchip is not usable.  
> 
> Could you please elaborate on this part?

I meant that is you start with large VCPU number but accelerator/irqchip
can't create correct (usable) VM, QEMU should exit with error.
 
> Thanks,
> Suravee
>