From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756291Ab3ENRhn (ORCPT ); Tue, 14 May 2013 13:37:43 -0400 Received: from 8bytes.org ([85.214.48.195]:52007 "EHLO mail.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752462Ab3ENRhm (ORCPT ); Tue, 14 May 2013 13:37:42 -0400 Date: Tue, 14 May 2013 19:37:39 +0200 From: Joerg Roedel To: "Paul E. McKenney" Cc: =?iso-8859-1?Q?Bj=F8rn?= Mork , "Paul E. McKenney" , linux-kernel@vger.kernel.org Subject: Re: Bisected post-3.9 regression: Resume takes 5 times as much time as with v3.9 Message-ID: <20130514173739.GH24440@8bytes.org> References: <87r4hdjsu5.fsf@nemi.mork.no> <20130512113157.GG3648@linux.vnet.ibm.com> <20130512182935.GD24440@8bytes.org> <20130512205747.GK3648@linux.vnet.ibm.com> <20130512213430.GE24440@8bytes.org> <20130513013518.GM3648@linux.vnet.ibm.com> <20130513140005.GA9165@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20130513140005.GA9165@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-DSPAM-Result: Whitelisted X-DSPAM-Processed: Tue May 14 19:37:40 2013 X-DSPAM-Confidence: 0.9988 X-DSPAM-Probability: 0.0000 X-DSPAM-Signature: 5192766423671048821419 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Mon, May 13, 2013 at 07:00:05AM -0700, Paul E. McKenney wrote: > rcu: Fix comparison sense in rcu_needs_cpu() > > Commit c0f4dfd4f (rcu: Make RCU_FAST_NO_HZ take advantage of numbered > callbacks) introduced a bug that can result in excessively long grace > periods. This bug reverse the senes of the "if" statement checking > for lazy callbacks, so that RCU takes a lazy approach when there are > in fact non-lazy callbacks. This can result in excessive boot, suspend, > and resume times. > > This commit therefore fixes the sense of this "if" statement. > > Reported-by: Borislav Petkov > Reported-by: Bjørn Mork > Reported-by: Joerg Roedel > Signed-off-by: Paul E. McKenney Just tested the patch, it fixes the long boot delay for me. Thanks for fixing this. Tested-by: Joerg Roedel > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 641991d..63098a5 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -1692,7 +1692,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj) > rdtp->last_accelerate = jiffies; > > /* Request timer delay depending on laziness, and round. */ > - if (rdtp->all_lazy) { > + if (!rdtp->all_lazy) { > *dj = round_up(rcu_idle_gp_delay + jiffies, > rcu_idle_gp_delay) - jiffies; > } else { >