Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755645Ab3ENAtU (ORCPT ); Mon, 13 May 2013 20:49:20 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:42055 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755472Ab3ENAtT (ORCPT ); Mon, 13 May 2013 20:49:19 -0400 Date: Mon, 13 May 2013 07:00:05 -0700 From: "Paul E. McKenney" To: Joerg Roedel 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: <20130513140005.GA9165@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20130513013518.GM3648@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13051400-2398-0000-0000-0000144E2238 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2151 Lines: 54 On Sun, May 12, 2013 at 06:35:18PM -0700, Paul E. McKenney wrote: > On Sun, May 12, 2013 at 11:34:30PM +0200, Joerg Roedel wrote: > > On Sun, May 12, 2013 at 01:57:48PM -0700, Paul E. McKenney wrote: > > > That does look pretty extreme! If you build with CONFIG_RCU_NO_HZ=n, > > > but without the revert, do you still get the delays? > > > > With CONFIG_RCU_NO_HZ=n (and no revert) the system boots fine, no boot > > delay. I also enabled some RCU debugging options (with > > CONFIG_RCU_NO_HZ=y), but didn't see anything so far. > > OK, good -- we at least have an easy work-around while I am tracking > this down. ;-) And could you please try out the following patch? Thanx, Paul ------------------------------------------------------------------------ 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: Bj?rn Mork Reported-by: Joerg Roedel Signed-off-by: Paul E. McKenney 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 { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/