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Re: [Xen-devel] VCPU migration overhead conpensation ?

On mer, 2013-04-10 at 09:21 +0100, George Dunlap wrote
> On 10/04/13 06:44, Sisu Xi wrote:
> > I am also performing some overhead measurement for the scheduler. If a 
> > VCPU is migrated from one core to another, the overhead is around 2 
> > microseconds on my machine, which is much less than what is set in 
> > Credit2 (50 microseconds).
> When you say "overhead", I assume you mean that's how long the whole 
> migration takes?
> The point of the compensation isn't so much for the actual migration 
> itself, but for the lower performance the vcpu will get after the 
> migration due to having cold caches.
Which is, BTW, right the effect that we were trying to measure
(although, again, it was Linux, not Xen at that time), with the
experiments I was describing in my e-mail...

Might have been obvious, but I think it's worth making it even more that
(thanks George :-) ), since I agree with George that _this_ is what we
should be concerned about, when it comes to migration.


<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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