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From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: kvm tools: clock sources for hrtimer
Date: Wed, 9 Nov 2011 20:14:31 +0400
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On Wed, Nov 09, 2011 at 08:00:06PM +0400, Cyrill Gorcunov wrote:
...
> > 
> > You'll need CONFIG_KVM_CLOCK.
> > 
> > I'm not actually sure how close our implementation is to having tsc
> > working so far, Cyrill knows more about that than me.
> > 
> 
> We dropped tsc while were debuggin timer interrupts and apic routing
> setup, it might be not needed already. (Still to be fair I'm not sure
> does kvm hypervisor has a control bit set for tsc and cause or not vm-exit).
> 
> In short -- you could drop this from command line and tell us how it goes ;)
> 

The history shows the following commit

| commit 513fa5b4ccba8f9a2270a4f5262433071456540b
| Author: Pekka Enberg <penberg@cs.helsinki.fi>
| Date:   Sun Apr 11 20:55:56 2010 +0300
|
|    kvm: Force 'notsc' and 'earlyprintk' kernel parameters
|    
|    We don't support TSC calibration properly and we want early printk so force
|    them as kernel parameters.
|    
|    Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

and as far as I remember it's because we were stuck at apic calibration,
but now we have an apic from kvm hypervisor so I think it's safe to drop it
now (but still should be tested more widely).

	Cyrill