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Re: [Xen-devel] Re: Xen scheduler

To: ncmike@xxxxxxxxxx
Subject: Re: [Xen-devel] Re: Xen scheduler
From: pak333@xxxxxxxxxxx
Date: Mon, 23 Apr 2007 19:33:57 +0000
Cc: "Mike D. Day" <ncmike@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thanks. A little more clarification.
 
Here is an example.
 
I have multiple VMs, each with 2 vcpus. There is no user affinity. So i will let the vcpus run whereever the Xen scheduler chooses. My system has 2 dual core sockets.
 
     If all 4 pcpus are idle, then will the scheduler assign the vcpus of a VM to the same socket pcpus.
     If while running, 2 pcpus from different sockets become available, the scheduler will assign 2 vcpus to those two pcpus. Does the scheduler do any optimization as to moving the vcpus of a vm to the same socket or just assign the vcpus as they become ready.
 
or if 3 pcpus are idle will the scheduler assign vcpus from a VM to the same socket.
 
Basically all my questions boil down to this: Does the Scheduler know about the pcpu layout(same socket) and does it do any scheduling based on that.
 
Thanks
Prabha
 
 
 
     
 
 
-------------- Original message --------------
From: "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_setvc puaffinity:
> 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
> PGP key: http://www.ncultra.org/ncmike/pubkey.asc
>
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