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

Suravee Suthikulpanit posted 3 patches 2 years, 8 months ago
Maintainers: "Michael S. Tsirkin" <mst@redhat.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Eduardo Habkost <eduardo@habkost.net>
There is a newer version of this series
[PATCH v5 3/3] pc: q35: Bump max_cpus to 1024
Posted by Suravee Suthikulpanit 2 years, 8 months ago 
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

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(-)

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 371cca7484..63866a16e0 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -360,12 +360,12 @@ 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->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);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
-    m->max_cpus = 288;
 }
 
 static void pc_q35_8_1_machine_options(MachineClass *m)
@@ -388,6 +388,7 @@ static void pc_q35_8_0_machine_options(MachineClass *m)
 
     /* For pc-q35-8.0 and older, use SMBIOS 2.8 by default */
     pcmc->default_smbios_ep_type = SMBIOS_ENTRY_POINT_TYPE_32;
+    m->max_cpus = 288;
 }
 
 DEFINE_Q35_MACHINE(v8_0, "pc-q35-8.0", NULL,
-- 
2.34.1
Re: [PATCH v5 3/3] pc: q35: Bump max_cpus to 1024
Posted by Igor Mammedov 2 years, 8 months ago 
On Tue, 6 Jun 2023 21:49:39 -0500
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> 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
> 
> 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>

Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  hw/i386/pc_q35.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index 371cca7484..63866a16e0 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -360,12 +360,12 @@ 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->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);
>      machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);
>      machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
> -    m->max_cpus = 288;
>  }
>  
>  static void pc_q35_8_1_machine_options(MachineClass *m)
> @@ -388,6 +388,7 @@ static void pc_q35_8_0_machine_options(MachineClass *m)
>  
>      /* For pc-q35-8.0 and older, use SMBIOS 2.8 by default */
>      pcmc->default_smbios_ep_type = SMBIOS_ENTRY_POINT_TYPE_32;
> +    m->max_cpus = 288;
>  }
>  
>  DEFINE_Q35_MACHINE(v8_0, "pc-q35-8.0", NULL,
Re: [PATCH v5 3/3] pc: q35: Bump max_cpus to 1024
Posted by Philippe Mathieu-Daudé 2 years, 8 months ago 
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(-)
Re: [PATCH v5 3/3] pc: q35: Bump max_cpus to 1024
Posted by Igor Mammedov 2 years, 8 months ago 
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(-)  
>
Re: [PATCH v5 3/3] pc: q35: Bump max_cpus to 1024
Posted by Daniel P. Berrangé 2 years, 8 months ago 
On Wed, Jun 07, 2023 at 10:26:59AM +0200, Philippe Mathieu-Daudé 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)
> 
> $ uname -srvp
> Linux 5.15.0-71-generic #78-Ubuntu SMP Tue Apr 18 09:00:29 UTC 2023 x86_64

That's a relatively old kernel. With latest kernels, the 'recommended cpus'
limit reported will match the number of CPUs in your host, so for me it
always complains for smp > 12.



With regards,
Daniel
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