linux-kernel - Re: [PATCH 3/3] aarch64: kvm: introduce CONFIG_KVM_MAX

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Date:	Tue, 17 Sep 2013 22:34:28 +0100
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Andrew Jones <drjones@...hat.com>
Cc:	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
	catalin.marinas@....com, gleb@...hat.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	marc.zyngier@....com, pbonzini@...hat.com, linux@....linux.org.uk,
	will.deacon@....com
Subject: Re: [PATCH 3/3] aarch64: kvm: introduce CONFIG_KVM_MAX_VCPUS

On Sat, Sep 14, 2013 at 02:10:56PM +0200, Andrew Jones wrote:
> Take CONFIG_KVM_MAX_VCPUS from arm32, but set the default to 8.
> 
> Signed-off-by: Andrew Jones <drjones@...hat.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  7 ++++++-
>  arch/arm64/kvm/Kconfig            | 11 +++++++++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 0859a4ddd1e7d..d1af8c49a5ca4 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -26,7 +26,12 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_mmio.h>
>  
> -#define KVM_MAX_VCPUS 4
> +#if defined(CONFIG_KVM_MAX_VCPUS)
> +#define KVM_MAX_VCPUS CONFIG_KVM_MAX_VCPUS
> +#else
> +#define KVM_MAX_VCPUS 0
> +#endif
> +
>  #define KVM_USER_MEM_SLOTS 32
>  #define KVM_PRIVATE_MEM_SLOTS 4
>  #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 21e90820bd23c..c9924b02e84f7 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -35,6 +35,17 @@ config KVM_ARM_HOST
>  	---help---
>  	  Provides host support for ARM processors.
>  
> +config KVM_MAX_VCPUS
> +	int "Number maximum supported virtual CPUs per VM"
> +	depends on KVM_ARM_HOST
> +	default 8

That data structure gets really big with 8 max vcpus.  I think we should
keep this at 4 for now, a quad-core VM is quite reasonable for now.

> +	help
> +	  Static number of max supported virtual CPUs per VM.
> +
> +	  The default is set to the highest number of vcpus that
> +	  current hardware supports. Set to a lower number to save
> +	  some resources. Set to a higher number to test scalability.
> +
>  config KVM_ARM_VGIC
>  	bool
>  	depends on KVM_ARM_HOST && OF
> -- 
> 1.8.1.4
> 

-- 
Christoffer
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