Re: [PATCH 7/7] KVM: VMX: Skip delta_tsc shift-and-divide if the dividend is zero

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> On 12 Apr 2019, at 23:18, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote:
> 
> Ten percent of nothin' is... let me do the math here.  Nothin' into
> nothin', carry the nothin'...
> 
> Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

I think you should explicitly state in commit message title that this is an optimisation. A rather small one I must say :)
Having said that:
Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>

-Liran

> ---
> arch/x86/kvm/vmx/vmx.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index a3211e3ee679..2fec11bc0ac9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7050,10 +7050,9 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
> 
> 	/* Convert to host delta tsc if tsc scaling is enabled */
> 	if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio &&
> -			u64_shl_div_u64(delta_tsc,
> +	    delta_tsc && u64_shl_div_u64(delta_tsc,
> 				kvm_tsc_scaling_ratio_frac_bits,
> -				vcpu->arch.tsc_scaling_ratio,
> -				&delta_tsc))
> +				vcpu->arch.tsc_scaling_ratio, &delta_tsc))
> 		return -ERANGE;
> 
> 	/*
> -- 
> 2.21.0
> 





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