linux-kernel - Re: [PATCH] KVM: Optimize kvm_arch_vcpu_ioctl

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Date:   Mon, 13 Apr 2020 09:56:17 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Optimize kvm_arch_vcpu_ioctl_run function

Tianjia,

On 2020-04-13 04:45, Tianjia Zhang wrote:
> kvm_arch_vcpu_ioctl_run() is only called in the file kvm_main.c,
> where vcpu->run is the kvm_run parameter, so it has been replaced.
> 
> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> ---
>  arch/x86/kvm/x86.c | 8 ++++----
>  virt/kvm/arm/arm.c | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3bf2ecafd027..70e3f4abbd4d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8726,18 +8726,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> *vcpu, struct kvm_run *kvm_run)
>  		r = -EAGAIN;
>  		if (signal_pending(current)) {
>  			r = -EINTR;
> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
> +			kvm_run->exit_reason = KVM_EXIT_INTR;
>  			++vcpu->stat.signal_exits;
>  		}
>  		goto out;
>  	}
> 
> -	if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
> +	if (kvm_run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
>  		r = -EINVAL;
>  		goto out;
>  	}
> 
> -	if (vcpu->run->kvm_dirty_regs) {
> +	if (kvm_run->kvm_dirty_regs) {
>  		r = sync_regs(vcpu);
>  		if (r != 0)
>  			goto out;
> @@ -8767,7 +8767,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> *vcpu, struct kvm_run *kvm_run)
> 
>  out:
>  	kvm_put_guest_fpu(vcpu);
> -	if (vcpu->run->kvm_valid_regs)
> +	if (kvm_run->kvm_valid_regs)
>  		store_regs(vcpu);
>  	post_kvm_run_save(vcpu);
>  	kvm_sigset_deactivate(vcpu);
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 48d0ec44ad77..ab9d7966a4c8 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -659,7 +659,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
>  		return ret;
> 
>  	if (run->exit_reason == KVM_EXIT_MMIO) {
> -		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
> +		ret = kvm_handle_mmio_return(vcpu, run);
>  		if (ret)
>  			return ret;
>  	}

Do you have any number supporting the idea that you are optimizing 
anything
here? Performance, code size, register pressure or any other relevant 
metric?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...