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

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 7 Jun 2023 10:26:59 +0200
Philippe Mathieu-Daudé <philmd@linaro.org> wrote:

> 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)

Also do not forget about TCG where KVM accel is not even in the picture.

> $ 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(-)  
>