Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756120Ab3D0QVC (ORCPT ); Sat, 27 Apr 2013 12:21:02 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:60530 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753035Ab3D0QU5 (ORCPT ); Sat, 27 Apr 2013 12:20:57 -0400 Date: Sat, 27 Apr 2013 09:20:49 -0700 From: "Paul E. McKenney" To: Julian Anastasov Cc: Eric Dumazet , Peter Zijlstra , Simon Horman , Ingo Molnar , lvs-devel@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org, Pablo Neira Ayuso , Dipankar Sarma , dhaval.giani@gmail.com Subject: Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections Message-ID: <20130427162049.GB3780@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1366940708-10180-1-git-send-email-horms@verge.net.au> <1366940708-10180-3-git-send-email-horms@verge.net.au> <20130426080313.GC8669@dyad.programming.kicks-ass.net> <20130426154547.GC3860@linux.vnet.ibm.com> <20130426171948.GA31467@dyad.programming.kicks-ass.net> <20130426174815.GI3860@linux.vnet.ibm.com> <1367000815.8964.243.camel@edumazet-glaptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13042716-7182-0000-0000-0000066E70FF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1677 Lines: 56 On Sat, Apr 27, 2013 at 02:32:48PM +0300, Julian Anastasov wrote: > > Hello, > > On Fri, 26 Apr 2013, Eric Dumazet wrote: > > > On Fri, 2013-04-26 at 10:48 -0700, Paul E. McKenney wrote: > > > > > Don't get me wrong, I am not opposing cond_resched_rcu_lock() because it > > > will be difficult to validate. For one thing, until there are a lot of > > > them, manual inspection is quite possible. So feel free to apply my > > > Acked-by to the patch. > > > > One question : If some thread(s) is(are) calling rcu_barrier() and > > waiting we exit from rcu_read_lock() section, is need_resched() enough > > for allowing to break the section ? > > > > If not, maybe we should not test need_resched() at all. > > > > rcu_read_unlock(); > > cond_resched(); > > rcu_read_lock(); > > So, I assume, to help realtime kernels and rcu_barrier > it is not a good idea to guard rcu_read_unlock with checks. > I see that rcu_read_unlock will try to reschedule in the > !CONFIG_PREEMPT_RCU case (via preempt_enable), can we > use ifdefs to avoid double TIF_NEED_RESCHED check?: > > rcu_read_unlock(); > #if !defined(CONFIG_PREEMPT) || defined(CONFIG_PREEMPT_RCU) I would instead suggest something like: #ifndef CONFIG_PREEMPT_RCU But yes, in the CONFIG_PREEMPT_RCU case, the cond_resched() is not needed. Thanx, Paul > cond_resched(); > #endif > rcu_read_lock(); > > Regards > > -- > Julian Anastasov > -- 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/