Re: [Xen-devel] Re: Live migration fails due to c/s 20627

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 12/16/2009 07:20 AM, Dan Magenheimer wrote:
> Well, "heuristic" implies a reasonably high probability of
> getting the right answer.  Would you agree that the probability
> that TSC_AUX gets the "right" answer is much higher
> in a physical environment than in a (non-pinned) virtual
> environment?  And if the heuristic is wrong more often
> than right, that using that heuristic is a bad idea?
>    
It won't make a difference either way.  Running in a Xen domain, the 
kernel will only see a single NUMA node, so the node id is constant.  
The CPU number may not correspond to a pcpu all the time, but scheduler 
affinity should make a given vcpu number correspond to the same pcpu for 
a while.
In either case, an application paying attention to cpu+node will do at 
least as well as an app ignoring them.  So I don't think your argument 
that "if TSC_AUX cannot ALWAYS be trusted by an application, apps will 
NEVER trust it" is true at all.
Aside from the fact that the cpu+node issue is completely irrelevant to 
whether we support TSC_AUX.
    J

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