Re: [PATCH v5] pc: q35: Bump max_cpus to 4096 vcpus

[Zhao Liu <zhao1.liu@intel.com>]

On Wed, Feb 28, 2024 at 08:03:51PM +0530, Ani Sinha wrote:
> Date: Wed, 28 Feb 2024 20:03:51 +0530
> From: Ani Sinha <anisinha@redhat.com>
> Subject: [PATCH v5] pc: q35: Bump max_cpus to 4096 vcpus
> X-Mailer: git-send-email 2.42.0
> 
> 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 <berrange@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Julia Suvorova <jusual@redhat.com>
> Cc: kraxel@redhat.com
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Ani Sinha <anisinha@redhat.com>
> ---
>  hw/i386/pc_q35.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>