From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: Re: Benchmarking on CentOS 5 Date: Wed, 28 May 2008 20:33:52 +0200 Message-ID: <20080528183352.GE8086@duo.random> References: <483D9AE5.6040509@cs.ualberta.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org To: Cam Macdonell Return-path: Received: from host36-195-149-62.serverdedicati.aruba.it ([62.149.195.36]:57779 "EHLO mx.cpushare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752139AbYE1Sdy (ORCPT ); Wed, 28 May 2008 14:33:54 -0400 Content-Disposition: inline In-Reply-To: <483D9AE5.6040509@cs.ualberta.ca> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, May 28, 2008 at 11:48:21AM -0600, Cam Macdonell wrote: > > Hi, > > I wanted to some benchmarking on a CentOS 5 host. However, the warning in > dmesg about preempt notifiers indicates I shouldn't benchmark. Is there a > workaround (aside from updating the kernel) that handles the issue? The problem is that the preempt notifier emulation through hardware breakpoints is worse at optimizing lightweight vm exists than the real preempt notifiers supported by recent kernels. If you benchmark without upgrading the kernel, it has to be clear it is running slower than it would on a recent optimized host kernel. If you decide to upgrade and compile the host kernel yourself, you need to configure it with CONFIG_KVM=m to be sure the preempt notifiers are enabled in the host kernel and in turn the printk will go away. Thanks!