linux-kernel - Re: [PATCH 1/5] Add a global synchronization point for pvclock

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Date:	Tue, 20 Apr 2010 14:07:46 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Avi Kivity <avi@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On 04/20/2010 09:42 AM, Jeremy Fitzhardinge wrote:
> On 04/20/2010 11:54 AM, Avi Kivity wrote:
>    
>> On 04/20/2010 09:23 PM, Jeremy Fitzhardinge wrote:
>>      
>>> On 04/20/2010 02:31 AM, Avi Kivity wrote:
>>>
>>>        
>>>> btw, do you want this code in pvclock.c, or shall we keep it kvmclock
>>>> specific?
>>>>
>>>>          
>>> I think its a pvclock-level fix.  I'd been hoping to avoid having
>>> something like this, but I think its ultimately necessary.
>>>
>>>        
>> Did you observe drift on Xen, or is this "ultimately" pointing at the
>> future?
>>      
> People are reporting weirdnesses that "clocksource=jiffies" apparently
> resolves.  Xen and KVM are faced with the same hardware constraints, and
> it wouldn't surprise me if there were small measurable
> non-monotonicities in the PV clock under Xen.  May as well be safe.
>    

Does the drift only occur on SMP VMs?

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