[Xen-devel] Re: Xen scheduler

["Mike D. Day" <ncmike@xxxxxxxxxx>]

On 21/04/07 06:03 +0000, pak333@xxxxxxxxxxx wrote:
>   Hi,
>
>
>
>   On running on a dual/quad core does the Xen scheduler take into
>   account the physical layout of the cores.
>
>   For example if a VM has two vcpus, and there are 4 physical cpus
>   free,  will it take care to assign the 2vcpus (from a VM) to 2 pcpus
>   on the same socket.

The scheduler only knows the affinity of vcpus for physical
cpus. The affinity is determined by a userspace application and can
be modified using a domain control hypercall. Look in
xen/common/domctl.c around line 568 for the following: 

   case XEN_DOMCTL_setvcpuaffinity:
   case XEN_DOMCTL_getvcpuaffinity:



When the credit scheduler migrates a vcpu to a pcpu, it only considers
pcpus for which the affinity bit is set. If the userspace application
sets affinity such that only the bits set for pcpus on the same
socket, then the vcpu will only run on pcpu's sharing the same
socket. 

Mike

--
Mike D. Day
IBM LTC
Cell: 919 412-3900
Sametime: ncmike@xxxxxxxxxx AIM: ncmikeday  Yahoo: ultra.runner
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