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Re: [Xen-devel] RE: [PATCH] rendezvous-based local time calibration WOW!

On Wed, Aug 6, 2008 at 11:21 AM, John Levon <levon@xxxxxxxxxxxxxxxxx> wrote:
> On Wed, Aug 06, 2008 at 09:09:06AM -0600, Dan Magenheimer wrote:
>> Again no guarantees but I think we are now under the magic
>> threshold where the skew is smaller than the time required
>> for scheduling a VCPU onto a different CPU.  If so,
>> consecutive gethrtime's by the same thread in a domain
>> should always be monotonic.
> Right! That sounds positive.

It's an improvement, but I'm pretty sure it's still not sufficient for
Solaris.  If I understand the change correctly, it seems to solve the
problem for single-vcpu guests on an SMP,  but not for multi-vcpu
guests on an SMP.  It sounds like the OS could reschedule a thread
from VCPU 0 to VCPU 1 and consecutive calls to gethrtime() could still
return non-monotonic results.


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