From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 1/2] xl: neuter vcpu-set --ignore-host. Date: Thu, 26 Sep 2013 17:01:26 +0100 Message-ID: <52445A56.6060505@citrix.com> References: <1380141617-8981-1-git-send-email-konrad.wilk@oracle.com> <1380141617-8981-2-git-send-email-konrad.wilk@oracle.com> <1380186391.29483.18.camel@kazak.uk.xensource.com> <20130926152800.GD6538@konrad-lan.dumpdata.com> <1380210460.29483.134.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1380210460.29483.134.camel@kazak.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: George.Dunlap@eu.citrix.com, xen-devel@lists.xensource.com, Ian.Jackson@eu.citrix.com List-Id: xen-devel@lists.xenproject.org On 26/09/13 16:47, Ian Campbell wrote: > On Thu, 2013-09-26 at 11:28 -0400, Konrad Rzeszutek Wilk wrote: >>>> - The user can already boot a massively overcommitted guest by >>>> having a large 'vcpus=' value in the guest config and we allow >>>> that. >>> IMHO this is an xl bug, I'd be happy to see a patch to fix this and >>> require and override here too. >> I actually think that doing vCPU overcommit is an OK process. If you go >> down the path of 'don't do this b/c it can cause performance degredation' >> you might end up with tons of things that we should be turning off: >> - don't use file but use phy for block. >> - if you have 40GB SR-IOV, use that instead of vif. >> - booting PV? You should be booting it in HVM mode on latest machines. >> - etc. > Those are all legitimate choices for a user to make. > > Overcommitting VCPUs is not. Depends how the overcommitting happens. What about: * User creating N VMs which are individually undercomitted but has the same effect as creating 1 VM which is stupidly overcommitted. * Power management decides to shut down some of the PCPUs because it can service all the current VCPUs from some somewhat idle domains on fewer PCPUs While I agree that creating a single VM which is overcommitted in terms of VCPUs is either a user error or power-user, that alone is not a justification for it being impossible/very hard to do. My two cents. ~Andrew