From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Fjellstrom Subject: Re: kvm linux guest hanging for minutes at a time Date: Thu, 11 Aug 2011 10:37:29 -0600 Message-ID: <201108111037.29798.thomas@fjellstrom.ca> References: <201108070806.59194.thomas@fjellstrom.ca> <4E41534F.1010502@letterboxes.org> <4E437901.9070207@redhat.com> Reply-To: thomas@fjellstrom.ca Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Nick , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Received: from mail.tomasu.net ([64.85.170.232]:40044 "EHLO mail.tomasu.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750825Ab1HKQhe (ORCPT ); Thu, 11 Aug 2011 12:37:34 -0400 In-Reply-To: <4E437901.9070207@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On August 11, 2011, Avi Kivity wrote: > On 08/09/2011 06:33 PM, Nick wrote: > > Hi, > > > > Just joined this list, looking for leads to solve a similar-sounding > > problem (guest processes hanging for seconds or minutes when host IO > > load is high). I'll say more in a separate email, but I caught the end > > of this thread and wanted to ask about kvm-clock. > > > > Naively I'd have thought that using the wrong clock would not actually > > *cause* hangs like this. Or is that what you're implying? > > Using the wrong clock easily causes hangs. The system schedules a > wakeup in 3 ms, wrong clock causes it to wakeup in 3 years, you get a > hang for (3 years - 3 ms). I am wondering though why the system time would be used to schedule wakeups when something a little more like the posix CLOCK_MONOTONIC would make more sense. You (at least I don't think you do) really don't want host clock changes to interfere with a guest so much that it sleeps forever. -- Thomas Fjellstrom thomas@fjellstrom.ca