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Re: [PATCH] pc: q35: Bump max_cpus to 512
From: |
Igor Mammedov |
Subject: |
Re: [PATCH] pc: q35: Bump max_cpus to 512 |
Date: |
Thu, 19 May 2022 14:37:54 +0200 |
On Thu, 19 May 2022 13:53:49 +0700
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> wrote:
> On 5/13/22 6:23 PM, Michael S. Tsirkin wrote:
> > 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.
> >
> > So what happens if one does 710 and then tries to use AMD x2APIC?
> > We'd like that to error out, right?
> >
>
> Since the AMD SVM x2AVIC can support only upto 512 vCPUs,
> KVM would return error when QEMU tries to create more than 512 vcpus
> in the following call-path:
>
> kvm_vm_ioctl_create_vcpu
> kvm_arch_vcpu_create
> svm_vcpu_create
> avic_init_vcpu
what is actual error message that end user will get from that failure?
> Also, I tried to find a way to get the KVM VCPU max value via
> KVM_CAP_MAX_VCPUS ioctl,
> but the accel/kvm/kvm-all.c:kvm_init() is called later than
> hw/core/machine-smp.c:
> machine_parse_smp_config(), where it checks the specified QEMU -smp option.
>
> So, if there is no objection, I will send out a patch to change m->max_cpus =
> 1024
> to match current KVM limit.
>
> Best Regards,
> Suravee
>
- Re: [PATCH] pc: q35: Bump max_cpus to 512, (continued)
Re: [PATCH] pc: q35: Bump max_cpus to 512, Michael S. Tsirkin, 2022/05/13