linux-kernel - Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read

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Message-ID: <20160607131621.GA15012@MinfeideMacBook-Pro.local>
Date:	Tue, 7 Jun 2016 21:16:21 +0800
From:	Minfei Huang <mnghuan@...il.com>
To:	bp@...e.de, pbonzini@...hat.com, luto@...nel.org, hpa@...or.com,
	mingo@...hat.com, tglx@...utronix.de
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in
 function pvclock_read_flags

ping. Any comment is appreciate.

Thanks
Minfei

On 05/28/16 at 08:27P, Minfei Huang wrote:
> There is a generic function __pvclock_read_cycles to be used to get both
> flags and cycles. For function pvclock_read_flags, it's useless to get
> cycles value. To make this function be more effective, get this variable
> flags directly in function.
> 
> Signed-off-by: Minfei Huang <mnghuan@...il.com>
> ---
> v1:
> - Get rid of __pvclock_read_cycles according to Andy's suggestion
> ---
>  arch/x86/kernel/pvclock.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index 7f82fe0..06c58ce 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -61,11 +61,14 @@ void pvclock_resume(void)
>  u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
>  {
>  	unsigned version;
> -	cycle_t ret;
>  	u8 flags;
>  
>  	do {
> -		version = __pvclock_read_cycles(src, &ret, &flags);
> +		version = src->version;
> +		/* Make the latest version visible */
> +		smp_rmb();
> +
> +		flags = src->flags;
>  		/* Make sure that the version double-check is last. */
>  		smp_rmb();
>  	} while ((src->version & 1) || version != src->version);
> -- 
> 2.6.3
>