linux-kernel - Re: [PATCH 2/3] kvm: use this_cpu_xxx replace percpu

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Date:	Mon, 24 Oct 2011 10:50:08 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Christoph Lameter <cl@...two.org>, "tj@...nel.org" <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"jeremy@...source.com" <jeremy@...source.com>
Subject: Re: [PATCH 2/3] kvm: use this_cpu_xxx replace percpu_xxx funcs

On Thu, 2011-10-20 at 15:34 +0800, Alex,Shi wrote:
> percpu_xxx funcs are duplicated with this_cpu_xxx funcs, so replace them
> for further code clean up.
> 
> And in preempt safe scenario, __this_cpu_xxx funcs has a bit better
> performance since __this_cpu_xxx has no redundant preempt_disable()
> 

Avi: 
Would you like to give some comments of this? 

> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  arch/x86/kvm/x86.c |   14 +++++++-------
>  1 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 84a28ea..432c4bc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5024,15 +5024,15 @@ static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
>  
>  static int kvm_is_in_guest(void)
>  {
> -	return percpu_read(current_vcpu) != NULL;
> +	return __this_cpu_read(current_vcpu) != NULL;
>  }
>  
>  static int kvm_is_user_mode(void)
>  {
>  	int user_mode = 3;
>  
> -	if (percpu_read(current_vcpu))
> -		user_mode = kvm_x86_ops->get_cpl(percpu_read(current_vcpu));
> +	if (__this_cpu_read(current_vcpu))
> +		user_mode = kvm_x86_ops->get_cpl(__this_cpu_read(current_vcpu));
>  
>  	return user_mode != 0;
>  }
> @@ -5041,8 +5041,8 @@ static unsigned long kvm_get_guest_ip(void)
>  {
>  	unsigned long ip = 0;
>  
> -	if (percpu_read(current_vcpu))
> -		ip = kvm_rip_read(percpu_read(current_vcpu));
> +	if (__this_cpu_read(current_vcpu))
> +		ip = kvm_rip_read(__this_cpu_read(current_vcpu));
>  
>  	return ip;
>  }
> @@ -5055,13 +5055,13 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = {
>  
>  void kvm_before_handle_nmi(struct kvm_vcpu *vcpu)
>  {
> -	percpu_write(current_vcpu, vcpu);
> +	__this_cpu_write(current_vcpu, vcpu);
>  }
>  EXPORT_SYMBOL_GPL(kvm_before_handle_nmi);
>  
>  void kvm_after_handle_nmi(struct kvm_vcpu *vcpu)
>  {
> -	percpu_write(current_vcpu, NULL);
> +	__this_cpu_write(current_vcpu, NULL);
>  }
>  EXPORT_SYMBOL_GPL(kvm_after_handle_nmi);
>  


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