Re: [PATCH v5 3/3] pc: q35: Bump max_cpus to 1024

[Philippe Mathieu-Daudé]

On 7/6/23 04:49, Suravee Suthikulpanit wrote:
> Since KVM_MAX_VCPUS is currently defined to 1024 for x86 as shown in
> arch/x86/include/asm/kvm_host.h, update QEMU limits to the same number.
>
> In case KVM could not support the specified number of vcpus, QEMU would
> return the following error message:
>
>    qemu-system-x86_64: kvm_init_vcpu: kvm_get_vcpu failed (xxx): Invalid 
> argument

Odd, we already check the upper limit with KVM_CAP_NR_VCPUS.
See in kvm_init():

    /* check the vcpu limits */
    soft_vcpus_limit = kvm_recommended_vcpus(s);
    hard_vcpus_limit = kvm_max_vcpus(s);

When testing your series I get:

qemu-system-x86_64: -accel kvm: warning: Number of SMP cpus requested 
(1024) exceeds the recommended cpus supported by KVM (710)

$ uname -srvp
Linux 5.15.0-71-generic #78-Ubuntu SMP Tue Apr 18 09:00:29 UTC 2023 x86_64

> Also, keep max_cpus at 288 for machine version 8.0 and older.
>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Julia Suvorova <jusual@redhat.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>   hw/i386/pc_q35.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)