Re: [Xen-users] SMP and CPU hyperthreading

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

On Tuesday 19 April 2005 21:19, Lars E. D. Jensen | DCmedia wrote:
> > IIRC, on a two CPU system the numbering is as follows:
> > 0 : 1st hyperthread, 1st CPU
> > 1 : 2nd hyperthread, 1st CPU
> > 2 : 1st hyperthread, 2nd CPU
> > 3 : 2nd hyperthread, 2nd CPU
> >
> > If you don't want to use HT, just assign to 0 and 2 (for instance) and
> > then you'll only have one domain running on a physical CPU at any time.
>
> Ok, will this syntax do it in the configuration?
>
> cpu = 0,2
>
> And does it work in 2.0.5 stable too?

Sorry, I didn't express that clearly.  Let me put it another way: in -stable 
you can't give more than one hyperthread to a domain but you *can* have more 
than one domain per hyperthread.

The configuration you suggest above won't work because you can only give one 
logical processor to a domain.

If you want to run two domains on hyperthreads on the same CPU, you can assign 
one of them cpu = 0 and the other one to cpu = 1.  The two domains will run 
simultaneously in threads on that physical CPU.  If you only want one domain 
at a time to run on the CPU, you should specify cpu = 0 in both config files.  
The same applies for the hyperthreads on your second CPU (but with cpu = 2 
instead of 0 and cpu = 3 instead of 1).

HTH,
Mark

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