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

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Date:	Wed, 18 Sep 2013 09:21:55 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	Andrew Jones <drjones@...hat.com>, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, catalin.marinas@....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 Tue, Sep 17, 2013 at 10:34:28PM +0100, Christoffer Dall wrote:
> 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.
> 
Which data structure? vgic? IIRC with 8 vcpus it will be something like
500 bytes bigger then it is now.

--
			Gleb.
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