From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH 1/2] xl: neuter vcpu-set --ignore-host. Date: Thu, 26 Sep 2013 08:48:14 -0400 Message-ID: <20130926124814.GE5792@konrad-lan.dumpdata.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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1380186391.29483.18.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 Thu, Sep 26, 2013 at 10:06:31AM +0100, Ian Campbell wrote: > On Wed, 2013-09-25 at 16:40 -0400, Konrad Rzeszutek Wilk wrote: > > When Xen 4.3 was released we had a discussion whether we should > > allow the vcpu-set command to allow the user to set more than > > physical CPUs for a guest (it didn't). The author brought up: > > - Xend used to do it, > > IMHO xend is buggy here. If it were being maintained I encourage a patch > to file this particular sharp edge off. > > > - If a user wants to do it, let them do it, > > We do, we have an option for those who know what they are doing to use > in the tiny minority of cases where they need to do this. > > > - The original author of the change did not realize the > > side-effect his patch caused this and had no intention of changing it. > > a happy accident then. > > > - 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 think I posted one some time ago, but I don't recall anybody commenting on it. Will repost it. > > > > > Since we were close to the release we added --ignore-host parameter > > as a mechanism for a user to still set more vCPUs that the physical > > machine as a stop-gate. > > > > This patch keeps said option but neuters the check so that we > > can overcommit. In other words - by default the user is > > allowed to set as many vCPUs as they would like. > > and why would a naive user want to do this? non-naive users can use the > option if this is what they really want, and are probably grateful for > the catch if they didn't intend to overcommit, which is almost always > even for expert users. > > This change need far better rationalisation than "because xend did it" > and "because we can". IMHO. I am going to defer to George here. His viewpoint (I am going to probably mangle it up) was that - if the user wants to do, let him/her do it without us putting obstacles. And I think Ian Jackson was ambivalent here and was deferring to George. George? > > > > > Furthermore mention this parameter change in the man-page. > > > > Signed-off-by: Konrad Rzeszutek Wilk > > --- > > docs/man/xl.pod.1 | 15 ++++++++++++++- > > tools/libxl/xl_cmdimpl.c | 28 ++++++++++++---------------- > > tools/libxl/xl_cmdtable.c | 2 +- > > 3 files changed, 27 insertions(+), 18 deletions(-) > > > > diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1 > > index 5975d7b..1199d01 100644 > > --- a/docs/man/xl.pod.1 > > +++ b/docs/man/xl.pod.1 > > @@ -597,7 +597,7 @@ This command is only available for HVM domains. > > Moves a domain out of the paused state. This will allow a previously > > paused domain to now be eligible for scheduling by the Xen hypervisor. > > > > -=item B I I > > +=item B I