Re: [PATCH] x86: Raise the hard VCPU count limit

[Sasha Levin <levinsasha928@gmail.com>]

On Sat, 2011-07-09 at 15:25 +0300, Sasha Levin wrote:
> The patch raises the hard limit of VCPU count to 1024.
> 
> This will allow developers to easily work on scalability
> and will allow users to test high VCPU setups easily without
> patching the kernel.
> 
> To prevent possible issues with current setups, KVM_CAP_NR_VCPUS
> now returns the recommended VCPU limit (which is still 64) - this
> should be a safe value for everybody, while a new KVM_CAP_MAX_VCPUS
> returns the hard limit which is now 1024.
> 
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Suggested-by: Pekka Enberg <penberg@cs.helsinki.fi>
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---

Ping?

>  Documentation/virtual/kvm/api.txt |   11 +++++++++--
>  arch/x86/include/asm/kvm_host.h   |    3 ++-
>  arch/x86/kvm/x86.c                |    3 +++
>  include/linux/kvm.h               |    3 ++-
>  4 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 42542eb..84883a0 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -175,10 +175,17 @@ Parameters: vcpu id (apic id on x86)
>  Returns: vcpu fd on success, -1 on error
>  
>  This API adds a vcpu to a virtual machine.  The vcpu id is a small integer
> -in the range [0, max_vcpus).  You can use KVM_CAP_NR_VCPUS of the
> -KVM_CHECK_EXTENSION ioctl() to determine the value for max_vcpus at run-time.
> +in the range [0, max_vcpus). 
> +
> +The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of
> +the KVM_CHECK_EXTENSION ioctl() at run-time.
> +The maximum possible value for max_vcpus can be retrieved using the
> +KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time.
> +
>  If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4
>  cpus max.
> +If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is
> +same as the value returned from KVM_CAP_NR_VCPUS.
>  
>  4.8 KVM_GET_DIRTY_LOG (vm ioctl)
>  
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d2ac8e2..7db3e66 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -26,7 +26,8 @@
>  #include <asm/mtrr.h>
>  #include <asm/msr-index.h>
>  
> -#define KVM_MAX_VCPUS 64
> +#define KVM_MAX_VCPUS 1024
> +#define KVM_SOFT_MAX_VCPUS 64
>  #define KVM_MEMORY_SLOTS 32
>  /* memory slots that does not exposed to userspace */
>  #define KVM_PRIVATE_MEM_SLOTS 4
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 77c9d86..9766f46 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2006,6 +2006,9 @@ int kvm_dev_ioctl_check_extension(long ext)
>  		r = !kvm_x86_ops->cpu_has_accelerated_tpr();
>  		break;
>  	case KVM_CAP_NR_VCPUS:
> +		r = KVM_SOFT_MAX_VCPUS;
> +		break;
> +	case KVM_CAP_MAX_VCPUS:
>  		r = KVM_MAX_VCPUS;
>  		break;
>  	case KVM_CAP_NR_MEMSLOTS:
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 55ef181..077c193 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -457,7 +457,7 @@ struct kvm_ppc_pvinfo {
>  #define KVM_CAP_VAPIC 6
>  #define KVM_CAP_EXT_CPUID 7
>  #define KVM_CAP_CLOCKSOURCE 8
> -#define KVM_CAP_NR_VCPUS 9       /* returns max vcpus per vm */
> +#define KVM_CAP_NR_VCPUS 9       /* returns recommended max vcpus per vm */
>  #define KVM_CAP_NR_MEMSLOTS 10   /* returns max memory slots per vm */
>  #define KVM_CAP_PIT 11
>  #define KVM_CAP_NOP_IO_DELAY 12
> @@ -544,6 +544,7 @@ struct kvm_ppc_pvinfo {
>  #define KVM_CAP_TSC_CONTROL 60
>  #define KVM_CAP_GET_TSC_KHZ 61
>  #define KVM_CAP_PPC_BOOKE_SREGS 62
> +#define KVM_CAP_MAX_VCPUS 63       /* returns max vcpus per vm */
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  


-- 

Sasha.