> On 28-Feb-2024, at 20:03, Ani Sinha <anisi...@redhat.com> wrote:
>
> Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow
> up to 4096 vCPUs")
> Linux kernel can support upto a maximum number of 4096 vcpus when MAXSMP is
> enabled in the kernel. At present, QEMU has been tested to correctly boot a
> linux guest with 4096 vcpus using the current edk2 upstream master branch that
> has the fixes corresponding to the following two PRs:
>
> https://github.com/tianocore/edk2/pull/5410
> https://github.com/tianocore/edk2/pull/5418
>
> The changes merged into edk2 with the above PRs will be in the upcoming
> 2024-05
> release. With current seabios firmware, it boots fine with 4096 vcpus already.
> So bump up the value max_cpus to 4096 for q35 machines versions 9 and newer.
> Q35 machines versions 8.2 and older continue to support 1024 maximum vcpus
> as before for compatibility reasons.
>
> If KVM is not able to support the specified number of vcpus, QEMU would
> return the following error messages:
>
> $ ./qemu-system-x86_64 -cpu host -accel kvm -machine q35 -smp 1728
> qemu-system-x86_64: -accel kvm: warning: Number of SMP cpus requested (1728)
> exceeds the recommended cpus supported by KVM (12)
> qemu-system-x86_64: -accel kvm: warning: Number of hotpluggable cpus
> requested (1728) exceeds the recommended cpus supported by KVM (12)
> Number of SMP cpus requested (1728) exceeds the maximum cpus supported by KVM
> (1024)
>
> Cc: Daniel P. Berrangé <berra...@redhat.com>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Cc: Julia Suvorova <jus...@redhat.com>
> Cc: kra...@redhat.com
> Reviewed-by: Daniel P. Berrangé <berra...@redhat.com>
> Reviewed-by: Igor Mammedov <imamm...@redhat.com>
> Reviewed-by: Gerd Hoffmann <kra...@redhat.com>
> Signed-off-by: Ani Sinha <anisi...@redhat.com>
Ping .. who is picking this up? The soft code freeze starts today?
> ---
> hw/i386/pc_q35.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> Changelog:
> v5: mention the PRs in the commit message. Add tags.
> v4: tweaked commit message as per suggestion from danpb explicitly
> stating that 4096 vcpus work with edk2 fixes that are going to be
> available in the coming edk2 release.
> v3: bump up to 4096 vcpus. It has now been tested to work with edk2.
> See RH Jira: https://issues.redhat.com/browse/RHEL-22202
> v2: bump up the vcpu number to 1856. Add failure messages from ekd2 in
> the commit description.
>
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index 45a4102e75..df63a92b78 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -350,7 +350,7 @@ static void pc_q35_machine_options(MachineClass *m)
> m->default_nic = "e1000e";
> m->default_kernel_irqchip_split = false;
> m->no_floppy = 1;
> - m->max_cpus = 1024;
> + m->max_cpus = 4096;
> m->no_parallel = !module_object_class_by_name(TYPE_ISA_PARALLEL);
> machine_class_allow_dynamic_sysbus_dev(m, TYPE_AMD_IOMMU_DEVICE);
> machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
> @@ -371,6 +371,7 @@ static void pc_q35_8_2_machine_options(MachineClass *m)
> {
> pc_q35_9_0_machine_options(m);
> m->alias = NULL;
> + m->max_cpus = 1024;
> compat_props_add(m->compat_props, hw_compat_8_2, hw_compat_8_2_len);
> compat_props_add(m->compat_props, pc_compat_8_2, pc_compat_8_2_len);
> }
> --
> 2.42.0
>
