linux-kernel - Re: [PATCH 16/17] TSC reset compensation

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Message-ID: <20100616135211.GL19104@mothafucka.localdomain>
Date:	Wed, 16 Jun 2010 10:52:11 -0300
From:	Glauber Costa <glommer@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	avi@...hat.com, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/17] TSC reset compensation

On Mon, Jun 14, 2010 at 09:34:18PM -1000, Zachary Amsden wrote:
> Attempt to synchronize TSCs which are reset to the same value.  In the
> case of a reliable hardware TSC, we can just re-use the same offset, but
> on non-reliable hardware, we can get closer by adjusting the offset to
> match the elapsed time.
> 
> Signed-off-by: Zachary Amsden <zamsden@...hat.com>
> ---
>  arch/x86/kvm/x86.c |   34 ++++++++++++++++++++++++++++++++--
>  1 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8e836e9..cedb71f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -937,14 +937,44 @@ static inline void kvm_request_guest_time_update(struct kvm_vcpu *v)
>  	set_bit(KVM_REQ_CLOCK_SYNC, &v->requests);
>  }
>  
> +static inline int kvm_tsc_reliable(void)
> +{
> +	return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
> +		boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
> +		!check_tsc_unstable());
> +}
> +
why can't we re-use vmware TSC_RELIABLE flag?


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