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

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Date:	Tue, 27 Apr 2010 12:11:36 -0300
From:	Glauber Costa <glommer@...hat.com>
To:	Marcelo Tosatti <mtosatti@...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 Tue, Apr 27, 2010 at 10:40:13AM -0300, Marcelo Tosatti wrote:
> 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.
You tell me to drop it, avi tells me to write this, I am happy to pick
any one of the two options. Just don't want to get ping-ponged between
haveit-dropit.
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