From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753830AbeEWBTr (ORCPT ); Tue, 22 May 2018 21:19:47 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:39726 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753740AbeEWBTO (ORCPT ); Tue, 22 May 2018 21:19:14 -0400 X-Google-Smtp-Source: AB8JxZoK/c+LI+F/cp/rExcbXKmQeSHorF3FrAuvT1q6FhDaZk0nuNWf+fGgjOS6pyYGfNa2/yTOqA== Date: Tue, 22 May 2018 18:19:11 -0700 From: Joel Fernandes To: "Paul E. McKenney" Cc: Steven Rostedt , byungchul.park@lge.com, mathieu.desnoyers@efficios.com, Josh Triplett , Lai Jiangshan , linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: Tasks RCU vs Preempt RCU Message-ID: <20180523011911.GD55359@joelaf.mtv.corp.google.com> References: <20180519225905.GB134184@joelaf.mtv.corp.google.com> <20180520004938.GZ3803@linux.vnet.ibm.com> <20180520112843.57079857@grimm.local.home> <20180520191846.GA248075@joelaf.mtv.corp.google.com> <20180521215951.2d6abfcb@gandalf.local.home> <20180522045414.GG40541@joelaf.mtv.corp.google.com> <20180522083832.45353d5f@gandalf.local.home> <20180522160949.GU3803@linux.vnet.ibm.com> <20180522132700.68b6660d@gandalf.local.home> <20180522174711.GY3803@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180522174711.GY3803@linux.vnet.ibm.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 22, 2018 at 10:47:11AM -0700, Paul E. McKenney wrote: > On Tue, May 22, 2018 at 01:27:00PM -0400, Steven Rostedt wrote: > > On Tue, 22 May 2018 09:09:49 -0700 > > "Paul E. McKenney" wrote: > > > > > Just for the record, if you guys realy want to take over Tasks RCU, > > > I have no objections. For one thing, I don't anticipate any other use > > > cases for it (famous last words!). But you break it, you buy it! ;-) > > > > It really matters how much of a burden is RCU_tasks to RCU itself? If > > it causes a lot of headache for you, and it prevents you from cleaning > > up RCU or making it better, then I would be happy to take it out of RCU > > and maintain it separately myself. But if that's not the case, I'm happy > > with keeping it within the RCU umbrella. Which brings me to the > > question of what motivation does Joel have to remove it? > > The burden on me from Tasks RCU has been quite light, so no need for a > change from my end. > > Over to you, Joel! ;-) My motivation was I felt RCU-preempt already did the same thing (which I still believe it does) so its redundant. Although now I'm convinced from our earlier discussions that its not feasible to do an rcu_read_lock and rcu_read_unlock in trampoline code. Sorry I didn't mean you should really nuke RCU-tasks if it has a purpose, but I was more trying to understand what its purpose was that RCU-preempt didn't solve. That's all. And welcome back from Vacation Steve. I'm about to send v7 of my preempt/irq tracepoint patches so the timing seems great. I hope you will be able to take a look at them. thanks! - Joel