linux-kernel - Re: [PATCH v2 1/7] Enable pvclock flags in vcpu_time

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Date:	Wed, 05 May 2010 11:29:12 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	zamsden@...hat.com, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH v2 1/7] Enable pvclock flags in vcpu_time_info structure

On 05/03/2010 06:52 PM, Glauber Costa wrote:
> This patch removes one padding byte and transform it into a flags
> field. New versions of guests using pvclock will query these flags
> upon each read.
>
> Flags, however, will only be interpreted when the guest decides to.
> It uses the pvclock_valid_flags function to signal that a specific
> set of flags should be taken into consideration. Which flags are valid
> are usually devised via HV negotiation.
>
> Signed-off-by: Glauber Costa<glommer@...hat.com>
> CC: Jeremy Fitzhardinge<jeremy@...p.org>
> ---
>   arch/x86/include/asm/pvclock-abi.h |    3 ++-
>   arch/x86/include/asm/pvclock.h     |    1 +
>   arch/x86/kernel/pvclock.c          |    9 +++++++++
>   3 files changed, 12 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
> index 6d93508..ec5c41a 100644
> --- a/arch/x86/include/asm/pvclock-abi.h
> +++ b/arch/x86/include/asm/pvclock-abi.h
> @@ -29,7 +29,8 @@ struct pvclock_vcpu_time_info {
>   	u64   system_time;
>   	u32   tsc_to_system_mul;
>   	s8    tsc_shift;
> -	u8    pad[3];
> +	u8    flags;
> +	u8    pad[2];
>   } __attribute__((__packed__)); /* 32 bytes */
>
>   struct pvclock_wall_clock {
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 53235fd..cd02f32 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -6,6 +6,7 @@
>
>   /* some helper functions for xen and kvm pv clock sources */
>   cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
> +void pvclock_set_flags(u8 flags);
>   unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
>   void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
>   			    struct pvclock_vcpu_time_info *vcpu,
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index 03801f2..aa2262b 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -31,8 +31,16 @@ struct pvclock_shadow_time {
>   	u32 tsc_to_nsec_mul;
>   	int tsc_shift;
>   	u32 version;
> +	u8  flags;
>   };
>
> +static u8 valid_flags = 0;
> +
>    

Minor optimization: __read_mostly.

-- 
error compiling committee.c: too many arguments to function

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