Re: [PATCH 0/5] Lazy fpu, cr0.ts

[Sheng Yang <sheng@linux.intel.com>]

On Thursday 31 December 2009 00:25:37 Avi Kivity wrote:
> There are currently some inefficiencies in how we virtualize the fpu and
>  cr0:
> 
> - we trap changes to cr0.ts unconditionally; however, when the guest fpu
>   is loaded, we're not really interested in cr0.ts (it's only needed when
>   the host fpu is loaded, to prevent the guest from accessing it)
> - we deactivate the fpu on every guest context switch, for no reason at all
> 
> Fix these issues by being as lazy as possible: deactivate the fpu at
> heavyweight context switch time, and when the fpu is active, give the guest
> ownership of cr0.ts.

Looks fine to me.

-- 
regards
Yang, Sheng

> 
> Joerg, I wasn't able to extend this to svm/npt.  If we switch to the guest
> with the host fpu loaded, then we must set cr0.ts and enable cr0
>  intercepts. I think this is much more expensive than keeping the guest fpu
>  active at all times.
> 
> Avi Kivity (5):
>   KVM: VMX: trace clts and lmsw instructions as cr accesses
>   KVM: Replace read accesses of vcpu->arch.cr0 by an accessor
>   KVM: VMX: Allow the guest to own some cr0 bits
>   KVM: Lazify fpu activation and deactivation
>   KVM: VMX: Give the guest ownership of cr0.ts when the fpu is active
> 
>  arch/x86/include/asm/kvm_host.h |    3 ++
>  arch/x86/kvm/emulate.c          |    6 ++--
>  arch/x86/kvm/kvm_cache_regs.h   |   12 +++++++++
>  arch/x86/kvm/mmu.c              |    2 +-
>  arch/x86/kvm/mmu.h              |    2 +-
>  arch/x86/kvm/svm.c              |   46
>  ++++++++++++++++++++++-------------- arch/x86/kvm/vmx.c              |  
>  48 ++++++++++++++++++++++++-------------- arch/x86/kvm/x86.c             
>  |   26 ++++++++++++---------
>  8 files changed, 93 insertions(+), 52 deletions(-)
>