From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: backport request for Xen 4.2 and 4.1 of cs 26287:127c2c47d440 Date: Fri, 08 Feb 2013 09:20:13 +0100 Message-ID: <5114B53D.1000108@ts.fujitsu.com> References: <51025526.3060105@ts.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51025526.3060105@ts.fujitsu.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 , Jan Beulich List-Id: xen-devel@lists.xenproject.org Ping? Am 25.01.2013 10:49, schrieb Juergen Gross: > Hi, > > I request backport of changeset 26287:127c2c47d440 to Xen 4.2 and Xen 4.1. > > Without this change we experience Dom0 lockups when cpupool0 has all > cpus but > one on a single socket and xen ticketlocks are disabled in Dom0. > > Some background information: > > Disabling ticketlocks in Dom0 was done to avoid lock starvation on certain > workloads with one lock in Dom0 taken at a higher frequency as ticketlock > processing would allow (the poll hypercall was much more expensive than > waiting > for the lock via spinning). In our configuration Dom0 is the only domain in > cpupool0 so using xen ticketlocks shouldn't be an advantage. > > The Dom0 lockup happened when one vcpu was holding the xtime_lock while all > other vcpus tried to grab it and none of the vcpus was running on the > single > core on the other socket. At some time all vcpus were spinning and the one > core was idle without being considered for vcpu migration (this should be > addressed by the changeset above). As none of the vcpus would give up > control > voluntarily the complete time slice is used with one vcpu of Dom0 having no > physical processor to run on. During that time the next timer interrupt > will > be pending leading to another request of the xtime_lock which will > trigger the > same loop over and over again. > > > Juergen > -- Juergen Gross Principal Developer Operating Systems PBG PDG 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