From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757086Ab2DDVgl (ORCPT ); Wed, 4 Apr 2012 17:36:41 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:40815 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756863Ab2DDVgk (ORCPT ); Wed, 4 Apr 2012 17:36:40 -0400 Date: Wed, 4 Apr 2012 14:36:33 -0700 From: "Paul E. McKenney" To: Josh Boyer Cc: linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org Subject: Re: RCU related performance regression in 3.3 Message-ID: <20120404213633.GI2302@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120404152726.GB16299@zod.bos.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120404152726.GB16299@zod.bos.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12040421-3352-0000-0000-000003D15D23 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Thanx, Paul