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Re: [Xen-devel] Cpu pools discussion

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Cpu pools discussion
From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date: Wed, 29 Jul 2009 07:47:46 +0200
Cc: George Dunlap <dunlapg@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, zhigang.x.wang@xxxxxxxxxx, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Delivery-date: Tue, 28 Jul 2009 22:48:14 -0700
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Dan Magenheimer wrote:
> Sorry for the late join...
> I wonder if cpu pools helps with the following problem:
> Some large software company that shall remain nameless
> continues to license their high value applications
> on a per-pcpu basis rather than on a per-vcpu basis.
> As a result, VMs running these applications must be
> restricted to specific pcpu's which are "licensed" to
> run the software.
> Currently this is done with pinning, but pinning
> does restrict the flexibility of a multi-vcpu VM.
> Affinity seems like it should help, but affinity
> doesn't restrict the VM from running on a non-affinitive
> pcpu (does it?)
> For example, assume you have an 8 vcpu VM and it
> must be restricted to a 2 pcpu license on a
> 4 pcpu server.  Ideally, you'd like any of the 8
> vcpus to be assigned to either pcpu at any time
> so you don't want to pin, for example, even
> vcpu's to pcpu#0 and odd vcpu's to pcpu#1.
> And, if all vcpus are idle, you'd like pcpu#0
> and pcpu#1 to be free to run other VMs.
> Can this be done with cpu pools (easier than / more
> flexibly than / and not at all ) with current pinning
> and affinity?

Pools will restrict the assigned domains to the assigned pcpus.
This can be done by affinity masks as well.
But pools won't allow domains of pool B to run on idle pcpus of pool A.

> Also in a data center, does cpu pools make it possible/
> easier for tools to pre-assign a subset of processors
> on ALL servers in the data center to serve a certain
> licensed class of VMs?  For example, perhaps one
> would like to upgrade some of the machines in one's
> virtual data center from dual-core to quad-core but
> not pay for additional per-pcpu app licenses (i.e.
> the additional pcpus will be used for other non-licensed
> VMs).  Tools could assign two pcpus on each server
> to be part of the "DB pool" thus restricting execution
> (and license fees) but still allowing easy migration.
> Can this be done with cpu pools (easier than / more
> flexibly than / and not at all ) with current pinning
> and affinity?

This is easy doable with pools.
We are doing this for our BS2000 system.

> If the answer to these questions is yes, than I
> suspect one large software company might be very
> interested in cpu pools.

Is one "yes" enough? :-)


Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 636 47950
Fujitsu Technolgy Solutions               e-mail: juergen.gross@xxxxxxxxxxxxxx
Otto-Hahn-Ring 6                        Internet: ts.fujitsu.com
D-81739 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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