Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] kvm:vmx:code changes in handle_io() to save some CPU
 cycles.
To:     Stephen Zhang <starzhangzsd@gmail.com>, seanjc@google.com,
        vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com,
        joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, x86@kernel.org, hpa@zytor.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1607588115-29971-1-git-send-email-starzhangzsd@gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <46f11275-c697-9c0b-a12b-152301acaa76@redhat.com>
Date:   Sat, 12 Dec 2020 01:34:47 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.4.0
MIME-Version: 1.0
In-Reply-To: <1607588115-29971-1-git-send-email-starzhangzsd@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 10/12/20 09:15, Stephen Zhang wrote:
> code changes in handle_io() to save some CPU cycles.
> 
> Signed-off-by: Stephen Zhang <starzhangzsd@gmail.com>
> ---
>   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 47b8357..109bcf64 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4899,15 +4899,14 @@ static int handle_triple_fault(struct kvm_vcpu *vcpu)
>   static int handle_io(struct kvm_vcpu *vcpu)
>   {
>   	unsigned long exit_qualification;
> -	int size, in, string;
> +	int size, in;
>   	unsigned port;
>   
>   	exit_qualification = vmx_get_exit_qual(vcpu);
> -	string = (exit_qualification & 16) != 0;
>   
>   	++vcpu->stat.io_exits;
>   
> -	if (string)
> +	if (exit_qualification & 16)
>   		return kvm_emulate_instruction(vcpu, 0);
>   
>   	port = exit_qualification >> 16;
> 

I would be very surprised if there's any change in the assembly code 
after this patch.

Paolo