From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752725Ab2DEMiF (ORCPT ); Thu, 5 Apr 2012 08:38:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62676 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692Ab2DEMiE (ORCPT ); Thu, 5 Apr 2012 08:38:04 -0400 Date: Thu, 5 Apr 2012 08:37:59 -0400 From: Josh Boyer To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org, pascal.chapperon@wanadoo.fr Subject: Re: RCU related performance regression in 3.3 Message-ID: <20120405123759.GE1963@zod.bos.redhat.com> References: <20120404152726.GB16299@zod.bos.redhat.com> <20120404213633.GI2302@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120404213633.GI2302@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 04, 2012 at 02:36:33PM -0700, Paul E. McKenney wrote: > On Wed, Apr 04, 2012 at 11:27:27AM -0400, Josh Boyer wrote: > > Hi Paul, > > > > We've had a few reports of some boot slowdowns with the 3.3 rebase we > > did in Fedora 16. One of our users volunteered to bisect a vanilla > > kernel and wound up at "rcu: Permit dyntick-idle with callbacks pending > > (commit 7cb924990)". You can find more details in the bug [1], but it's > > been reported on both physical hardware and in virtual machines. > > > > Have you seen anything like this in your testing? Given the user used a > > vanilla 3.3 kernel, I'm wondering if there is a targetted fix that might > > be backported. If so, it would be good to get that headed to the 3.3.y > > stable tree. > > > > josh > > > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=806548 > > I will look into this. In the meantime, does setting > CONFIG_RCU_FAST_NO_HZ=n get rid of the slowdowns? Seems so. Pascal tried 3.4-rc1 with and without that set and found that disabling it lead to consistent timings. He put his findings in the bug, and I've also now CC'd him. josh