From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [PATCH] xl cpupool-numa-split: reduce number of Dom0 vcpus Date: Wed, 16 Feb 2011 09:40:55 +0100 Message-ID: <4D5B8D97.4020505@ts.fujitsu.com> References: <4D592A6F.9040700@ts.fujitsu.com> <19801.19977.577959.1306@mariner.uk.xensource.com> <4D5A16E3.70000@ts.fujitsu.com> <19802.54190.181244.976489@mariner.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <19802.54190.181244.976489@mariner.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Jackson Cc: George Dunlap , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 02/15/11 20:27, Ian Jackson wrote: > Juergen Gross writes ("Re: [Xen-devel] [PATCH] xl cpupool-numa-split: reduce number of Dom0 vcpus"): >> I added a failure exit if not all required vcpus are offlined. > > Thanks. But, is this test correct ? > >> + if (info.vcpu_online == n) { >> + break; >> + } > > Is it possible for the online map to have n cpus in it, but for them > to be the wrong n cpus ? The number of online vcpus is important, not which vcpus. In a strange case it could lead to a wrong number of online vcpus, if the number was correct in the beginning and e.g. vcpu 0 was offline and offlining the last vcpu fails. But I don't think this would be a huge problem, as offlining the vcpus is just a optimization measure. > > What if two copies of this code run concurrently ? (Perhaps in 4.2 we > will need to add a lock?) The result of both copies should be the same, as it is depending on the machine configuration only. And we are speaking of a global machine configuration action. This would mean two administrators are configuring the same machine without knowing what the other is doing. Seems to be a very strange scenario. A possible failure (meaning: not reaching the desired configuration, but no crashing) should be regarded as acceptable in this case. Juergen -- Juergen Gross Principal Developer Operating Systems TSP ES&S SWE OS6 Telephone: +49 (0) 89 3222 2967 Fujitsu Technology Solutions e-mail: juergen.gross@ts.fujitsu.com Domagkstr. 28 Internet: ts.fujitsu.com D-80807 Muenchen Company details: ts.fujitsu.com/imprint.html