From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755843Ab3D0LkK (ORCPT ); Sat, 27 Apr 2013 07:40:10 -0400 Received: from ja.ssi.bg ([178.16.129.10]:46942 "EHLO ja.ssi.bg" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752637Ab3D0LkI (ORCPT ); Sat, 27 Apr 2013 07:40:08 -0400 X-Greylist: delayed 416 seconds by postgrey-1.27 at vger.kernel.org; Sat, 27 Apr 2013 07:40:07 EDT Date: Sat, 27 Apr 2013 14:32:48 +0300 (EEST) From: Julian Anastasov To: Eric Dumazet cc: paulmck@linux.vnet.ibm.com, 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 In-Reply-To: <1367000815.8964.243.camel@edumazet-glaptop> Message-ID: 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> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) cond_resched(); #endif rcu_read_lock(); Regards -- Julian Anastasov