From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752631AbaHBXA2 (ORCPT ); Sat, 2 Aug 2014 19:00:28 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:53823 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751911AbaHBXA1 (ORCPT ); Sat, 2 Aug 2014 19:00:27 -0400 Date: Sat, 2 Aug 2014 16:00:21 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, bobby.prani@gmail.com Subject: Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks() Message-ID: <20140802230020.GD8101@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140731215445.GA21933@linux.vnet.ibm.com> <1406843709-23396-1-git-send-email-paulmck@linux.vnet.ibm.com> <20140801141144.GA30293@redhat.com> <20140801182837.GI4784@linux.vnet.ibm.com> <20140801184059.GB10718@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140801184059.GB10718@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14080223-8236-0000-0000-000004503319 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 01, 2014 at 08:40:59PM +0200, Oleg Nesterov wrote: > On 08/01, Paul E. McKenney wrote: > > > > On Fri, Aug 01, 2014 at 04:11:44PM +0200, Oleg Nesterov wrote: > > > Not sure this makes any sense, but perhaps we can check for the new > > > callbacks and start the next gp. IOW, the main loop roughly does > > > > > > for (;;) { > > > list = rcu_tasks_cbs_head; > > > rcu_tasks_cbs_head = NULL; > > > > > > if (!list) > > > sleep(); > > > > > > synchronize_sched(); > > > > > > wait_for_rcu_tasks_holdout(); > > > > > > synchronize_sched(); > > > > > > process_callbacks(list); > > > } > > > > > > we can "join" 2 synchronize_sched's and do > > > > > > ready_list = NULL; > > > for (;;) { > > > list = rcu_tasks_cbs_head; > > > rcu_tasks_cbs_head = NULL; > > > > > > if (!list && !ready_list) > > > sleep(); > > > > > > synchronize_sched(); > > > > > > if (ready_list) { > > > process_callbacks(ready_list); > > > ready_list = NULL; > > > } > > > > > > if (!list) > > > continue; > > > > > > wait_for_rcu_tasks_holdout(); > > > ready_list = list; > > > } > > > > The lack of barriers for the updates I am checking mean that I really > > do need a synchronize_sched() on either side of the grace-period wait. > > Yes, > > > The grace period needs to guarantee that anything that happened on any > > CPU before the start of the grace period happens before anything that > > happens on any CPU after the end of the grace period. If I leave off > > either synchronize_sched(), we lose this guarantee. > > But the 2nd variant still has synchronize_sched() on both sides? Your second variant above? Unless it is in wait_for_rcu_tasks_holdouts(), I am not seeing it. Thanx, Paul