linux-kernel - Re: [PATCH 6/6] don't compute pvclock adjustments if we trust the tsc

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Message-ID: <20100427134013.GE18410@amt.cnet>
Date:	Tue, 27 Apr 2010 10:40:13 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH 6/6] don't compute pvclock adjustments if we trust the tsc

On Mon, Apr 26, 2010 at 01:46:28PM -0400, Glauber Costa wrote:
> If the HV told us we can fully trust the TSC, skip any
> correction
> 
> Signed-off-by: Glauber Costa <glommer@...hat.com>
> ---
>  arch/x86/include/asm/kvm_para.h    |    5 +++++
>  arch/x86/include/asm/pvclock-abi.h |    1 +
>  arch/x86/kernel/kvmclock.c         |    3 +++
>  arch/x86/kernel/pvclock.c          |    4 ++++
>  4 files changed, 13 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index f019f8c..615ebb1 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -21,6 +21,11 @@
>   */
>  #define KVM_FEATURE_CLOCKSOURCE2        3
>  
> +/* The last 8 bits are used to indicate how to interpret the flags field
> + * in pvclock structure. If no bits are set, all flags are ignored.
> + */
> +#define KVM_FEATURE_CLOCKSOURCE_STABLE_TSC	0xf8
> +
>  #define MSR_KVM_WALL_CLOCK  0x11
>  #define MSR_KVM_SYSTEM_TIME 0x12

Please drop this. Its not certain what is the best method to reduce
contention on the global variable. Whatever it is, can be done later.

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