Re: [Xen-devel] Re: Xen scheduler

[pak333@xxxxxxxxxxx]

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 
> > 
> > _______________________________________________ 
> > Xen-devel mailing list 
> > Xen-devel@xxxxxxxxxxxxxxxxxxx 
> > http://lists.xensource.com/xen-devel 
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