From mboxrd@z Thu Jan 1 00:00:00 1970 From: Romain LE DISEZ Subject: Host processes priority over guests Date: Tue, 17 Jan 2012 07:45:44 +0100 Message-ID: <4F151918.7040407@ledisez.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: kvm@vger.kernel.org Return-path: Received: from srv03.ledisez.netensia.net ([195.160.188.88]:57063 "EHLO srv03.ledisez.netensia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751886Ab2AQGwh (ORCPT ); Tue, 17 Jan 2012 01:52:37 -0500 Received: from iMac-de-Romain.local (van-int1-sia.telensia.net [46.18.96.146]) (Authenticated sender: romain@ledisez.net) by srv03.ledisez.netensia.net (Postfix) with ESMTPSA id B7EDD1224E50 for ; Tue, 17 Jan 2012 07:45:44 +0100 (CET) Sender: kvm-owner@vger.kernel.org List-ID: Hello all, we are currently evaluating a migration from Xen to KVM. We host our VMs on a SAN, access to LUNs is done by the iSCSI protocol, all multipathed. With Xen, we faced a problem when VMs were consuming a lot of CPU and a lot of I/O. In this situation, the Dom0 did not get enough CPU time to process the I/O requests through the iSCSI processes and to run the iscsid daemon. So, the Dom0 was always loosing the iSCSI connection to the SAN because of timeout (node.conn[0].timeo.noop_out_timeout). We solved it by dedicating a core to the Dom0, as recommended in the Xen FAQ. Can this happen with KVM ? Why can(not) it happen ? If it could happen, what is the recommended solution (renice, cgroups, ...) ? Thanks for your help. -- Romain LE DISEZ