From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755195AbaHFA5X (ORCPT ); Tue, 5 Aug 2014 20:57:23 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.225]:13297 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751081AbaHFA5W (ORCPT ); Tue, 5 Aug 2014 20:57:22 -0400 Date: Tue, 5 Aug 2014 20:57:11 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: Oleg Nesterov , 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, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, bobby.prani@gmail.com Subject: Re: [PATCH v3 tip/core/rcu 3/9] rcu: Add synchronous grace-period waiting for RCU-tasks Message-ID: <20140805205711.7a52076c@gandalf.local.home> In-Reply-To: <20140802225857.GC8101@linux.vnet.ibm.com> References: <20140731215445.GA21933@linux.vnet.ibm.com> <1406843709-23396-1-git-send-email-paulmck@linux.vnet.ibm.com> <1406843709-23396-3-git-send-email-paulmck@linux.vnet.ibm.com> <20140801150926.GA845@redhat.com> <20140801183251.GJ4784@linux.vnet.ibm.com> <20140801194417.GA27141@linux.vnet.ibm.com> <20140802144719.GA18018@redhat.com> <20140802225857.GC8101@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.24; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2 Aug 2014 15:58:57 -0700 "Paul E. McKenney" wrote: > On Sat, Aug 02, 2014 at 04:47:19PM +0200, Oleg Nesterov wrote: > > On 08/01, Paul E. McKenney wrote: > > > > > > On Fri, Aug 01, 2014 at 11:32:51AM -0700, Paul E. McKenney wrote: > > > > On Fri, Aug 01, 2014 at 05:09:26PM +0200, Oleg Nesterov wrote: > > > > > On 07/31, Paul E. McKenney wrote: > > > > > > > > > > > > +void synchronize_rcu_tasks(void) > > > > > > +{ > > > > > > + /* Complain if the scheduler has not started. */ > > > > > > + rcu_lockdep_assert(!rcu_scheduler_active, > > > > > > + "synchronize_rcu_tasks called too soon"); > > > > > > + > > > > > > + /* Wait for the grace period. */ > > > > > > + wait_rcu_gp(call_rcu_tasks); > > > > > > +} > > > > > > > > > > Btw, what about CONFIG_PREEMPT=n ? > > > > > > > > > > I mean, can't synchronize_rcu_tasks() be synchronize_sched() in this > > > > > case? > > > > > > > > Excellent point, indeed it can! > > > > > > > > And if I do it right, it will make CONFIG_TASKS_RCU=y safe for kernel > > > > tinification. ;-) > > > > > > Unless, that is, we need to wait for trampolines in the idle loop... > > > > > > Sounds like a question for Steven. ;-) > > > > Sure, but the full blown synchronize_rcu_tasks() can't handle the idle threads > > anyway. An idle thread can not be deactivated and for_each_process() can't see > > it anyway. > > Indeed, if idle threads need to be tracked, their tracking will need to > be at least partially special-cased. > Yeah, idle threads can be affected by the trampolines. That is, we can still hook a trampoline to some function in the idle loop. But we should be able to make the hardware call that puts the CPU to sleep a quiescent state too. May need to be arch dependent. :-/ -- Steve