From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [Patch] use full-size cpumask for vcpu-pin Date: Fri, 13 Aug 2010 14:15:45 +0100 Message-ID: References: <19557.17517.80641.81294@mariner.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <19557.17517.80641.81294@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: Juergen Gross , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 13/08/2010 14:11, "Ian Jackson" wrote: > Keir Fraser writes ("Re: [Xen-devel] [Patch] use full-size cpumask for > vcpu-pin"): >> Actually, now I look at it, I have to NACK the patch. Sorry I didn't look >> closely enough earlier. I think the bug can be addressed without any >> hypervisor changes: when vcpu-pinning, the tools can quite correctly pass a >> cpumask to Xen just big enough to express just the CPUs in the new affinity >> set. If the resulting mask is too narrow to address all CPUs in the system, >> then Xen will pad it out with zeroes. If the resulting mask is too wide, Xen >> will simply truncate it. All this is done silently at the time of the >> setvcpuaffinity hypercall. > > The difficulty is, as I understand it, how to express the mask "all > CPUs present and future". Since the number of pcpus may be very > large. The tools presumably shouldn't pass a kilobyte of 0xff :-). Since Xen discards any CPUs which are not online at the time of the setvcpuaffinity hypercall, expressing "all CPUs present and future" is a bit pointless. -- Keir