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

Zachary Amsden
2010-04-21T00:08:22Z

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?