Re: Xen credit scheduler question

[Dario Faggioli <raistlin@linux.it>]

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On Thu, 2012-11-15 at 19:52 +0000, George Dunlap wrote:

> 
> BTW, are you familiar with Xen's cpupool functionality?  The guys at
> Fujitsu wrote it so that a customer could rent a fixed number of cores
> to a customer, who could then run as many VMs on those cores as they
> wanted.  I think licensing restrictions had something to do with that
> as well.  More about that here, if you're interested:
>  http://blog.xen.org/index.php/2012/04/23/xen-4-2-cpupools/
>
That is true, and I was right about to suggest considering cpupools for
this discussion. However, since it seems you're interested in the
difference between 'core' and 'hyperthread', cpupools also see
hyperthreads as cpus (as almost every other piece of Xen, with the only
exception of that small bit of the load balancer, as explained by
George). So, if cpu0 and cpu1 are hyperthreads of the same core, and you
put them in the same pool, you're back to square 1 and you've got to
take the 0.7 factor into account.

It is probably possible to differentiate, during accounting, the time
spent on a (busy?) hyperthread wrt the time spent on a "regular" core,
but not without modifying the scheduler. Otherwise, if HT is disturbing
too much, I've seen people turning it off (different scope and purposes,
i.e., real-time, but still), provided the BIOS offers such an option.

Dario

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


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