Re: [PATCH] x86: kvm: introduce CONFIG_KVM_MAX_VCPUS

[Andrew Jones <drjones@redhat.com>]

On Sun, Sep 15, 2013 at 12:08:38PM +0300, Gleb Natapov wrote:
> On Sat, Sep 14, 2013 at 02:18:49PM +0200, Andrew Jones wrote:
> > Take CONFIG_KVM_MAX_VCPUS from arm32, but set the default to 255.
> > 
> > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  5 +++--
> >  arch/x86/kvm/Kconfig            | 10 ++++++++++
> >  2 files changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index c76ff74a98f2e..e7e9b523a8f7e 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -31,8 +31,9 @@
> >  #include <asm/msr-index.h>
> >  #include <asm/asm.h>
> >  
> > -#define KVM_MAX_VCPUS 255
> > -#define KVM_SOFT_MAX_VCPUS 160
> > +#define KVM_MAX_VCPUS CONFIG_KVM_MAX_VCPUS
> > +#define KVM_SOFT_MAX_VCPUS min(160, KVM_MAX_VCPUS)
> > +
> >  #define KVM_USER_MEM_SLOTS 125
> >  /* memory slots that are not exposed to userspace */
> >  #define KVM_PRIVATE_MEM_SLOTS 3
> > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> > index a47a3e54b964b..e9532c33527ee 100644
> > --- a/arch/x86/kvm/Kconfig
> > +++ b/arch/x86/kvm/Kconfig
> > @@ -52,6 +52,16 @@ config KVM
> >  
> >  	  If unsure, say N.
> >  
> > +config KVM_MAX_VCPUS
> > +	int "Number maximum supported virtual CPUs per VM"
> > +	depends on KVM
> > +	default 255
> > +	help
> > +	  Static number of max supported virtual CPUs per VM.
> > +
> > +	  Set to a lower number to save some resources. Set to a higher
> > +	  number to test scalability.
> > +
> Maximum this can save is around 2K per VM. This is pretty insignificant
> considering overall memory footprint even smallest VM has.

Should I reword this, dropping all 'save resources' verbiage, in order to
avoid sending a message that this option can affect resource consumption?
Or just leave it as it is, because even though it's insignificant, it's
still true and balances out the 'Set to a higher' part.

drew

> 
> >  config KVM_INTEL
> >  	tristate "KVM for Intel processors support"
> >  	depends on KVM
> > -- 
> > 1.8.1.4
> 
> --
> 			Gleb.