From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH v1 2/2] libxl: vcpu-set - allow to decrease vcpu count on overcommitted guests (v2) Date: Mon, 2 Feb 2015 15:47:45 -0500 Message-ID: <1422910069-15760-1-git-send-email-konrad.wilk@oracle.com> References: <1402045657.29759.34.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YINuf-0007kc-Ah for xen-devel@lists.xenproject.org; Mon, 02 Feb 2015 20:48:05 +0000 In-Reply-To: <1402045657.29759.34.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: xen-devel@lists.xenproject.org, Ian.Campbell@citrix.com, ian.jackson@eu.citrix.com, wei.liu2@citrix.com List-Id: xen-devel@lists.xenproject.org On Fri, Jun 06, 2014 at 10:07:37AM +0100, Ian Campbell wrote: > On Thu, 2014-06-05 at 13:44 -0400, Konrad Rzeszutek Wilk wrote: > > > > - /* NB: This also limits how many are set in the bitmap */ > > > > - max_vcpus = (max_vcpus > host_cpu ? host_cpu : max_vcpus); > > > > > > Where did this go? > > > > No need for it actually. As we already do the action if 'max_vcpus > > > host_cpu' - which is that we return. So in essence that code will set max_vcpus > > to max_vcpus. > > What about if dominfo.vcpu_online > max_vcpus? iN that case the > max_vcpus > host_cpu check doesn't occur. Let me split that change out to a different patch. But in case you do remember this conversation - that is the purpose of this patch - to bypass the check. > > You could be in this state if someone had previously forced overcommit I > think. Right, or the guest was constructed with values greater than pCPU. Since I am sure you don't remember the context of this patch, I am resending them here (they grew to four patches) Let me rehash what we had in set in stone way back in 4.4: - The guest config ('maxvcpus') is permitted to be greater than the pCPUs. Ditto for the initially allocated ('vcpus') amounts. It is also OK to be different - 'vcpus' < 'maxvcpus', etc. - If the 'vcpus' < pCPUs and we want to increase it above pCPUs we should error out and print out a warning telling them to use --ignore-host. Regardless of the dominfo.max_vcpu_id - so if the max_vpcu_id is greater than pCPU and 'vcpu' < pCPU, we should still warn the user when increasing. - If the 'vcpus' > pCPUs and we want to decrease to be below pCPUs then we should do that without the warning. (this is what the patch was fixing).