From mboxrd@z Thu Jan  1 00:00:00 1970
From: Scott Wood <scottwood@freescale.com>
Subject: Re: [RFC PATCH 6/6] KVM: PPC: Book3E: Enhance FPU laziness
Date: Tue, 4 Jun 2013 17:53:52 -0500
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References: <1370292868-2697-7-git-send-email-mihai.caraman@freescale.com>
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Cc: <kvm-ppc@vger.kernel.org>, <kvm@vger.kernel.org>,
	<linuxppc-dev@lists.ozlabs.org>,
	Mihai Caraman <mihai.caraman@freescale.com>
To: Mihai Caraman <mihai.caraman@freescale.com>
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In-Reply-To: <1370292868-2697-7-git-send-email-mihai.caraman@freescale.com>
	(from mihai.caraman@freescale.com on Mon Jun  3 15:54:28 2013)
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On 06/03/2013 03:54:28 PM, Mihai Caraman wrote:
> Adopt AltiVec approach to increase laziness by calling  
> kvmppc_load_guest_fp()
> just before returning to guest instaed of each sched in.
> 
> Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>

If you did this *before* adding Altivec it would have saved a question  
in an earlier patch. :-)

> ---
>  arch/powerpc/kvm/booke.c  |    1 +
>  arch/powerpc/kvm/e500mc.c |    2 --
>  2 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index 019496d..5382238 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -1258,6 +1258,7 @@ int kvmppc_handle_exit(struct kvm_run *run,  
> struct kvm_vcpu *vcpu,
>  		} else {
>  			kvmppc_lazy_ee_enable();
>  			kvmppc_load_guest_altivec(vcpu);
> +			kvmppc_load_guest_fp(vcpu);
>  		}
>  	}
> 

You should probably do these before kvmppc_lazy_ee_enable().

Actually, I don't think this is a good idea at all.  As I understand  
it, you're not supposed to take kernel ownersship of floating point in  
non-atomic context, because an interrupt could itself call  
enable_kernel_fp().

Do you have benchmarks showing it's even worthwhile?

-Scott