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Re: [Xen-devel] [PATCH] libxl: Make 'xl vcpu-set' work properly on overcommited hosts.

  • To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
  • From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
  • Date: Mon, 13 May 2013 07:00:07 +0200
  • Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>
  • Delivery-date: Mon, 13 May 2013 05:00:49 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

On 09.05.2013 00:39, Konrad Rzeszutek Wilk wrote:
Well, overcommit comes in mind. Say you migrate to a 4PCPU box and you
have 12VCPUs, then you decide to go down to 4, then back to 16 before
migrating it to some other box. Can't do.

You could do it *after* the migration back to a 16 way box n stead of
before though, which is most likely when you would actually want to do

I am kind of lost. Are we arguing for this being a bug or whether there is
justification for putting in Xen 4.3?

The former needs deciding before the latter.

I'm not convinced that the current xl behaviour of refusing to
overcommit VCPUs on a host isn't the right one for the majority of use
cases. Obviously the silently refusing bit is a bug which should be

I don't buy that this is a "regression compared to Xend". It's certainly
a difference from how xend behaved but it seems on the whole to be a
positive one (i.e. xend was wrong).

CC-ing Juergen here as he added this in.

I surely didn't mean to disable overcommitting. So I'm fine with your patch
to do the cpumap allocation with maxvcpus.


Juergen Gross                 Principal Developer Operating Systems
PBG PDG ES&S SWE OS6                   Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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