Re: VCPU migration overhead conpensation ?

[Dario Faggioli <dario.faggioli@citrix.com>]

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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.

Regards,
Dario

-- 
<<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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