From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757391Ab2EVDD3 (ORCPT ); Mon, 21 May 2012 23:03:29 -0400 Received: from ozlabs.org ([203.10.76.45]:48759 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752889Ab2EVDD0 (ORCPT ); Mon, 21 May 2012 23:03:26 -0400 From: Rusty Russell To: Thomas Gleixner Cc: "Srivatsa S. Bhat" , LKML , linux-arch@vger.kernel.org, Peter Zijlstra , "Paul E. McKenney" , Ingo Molnar , Nikunj A Dadhania , Steven Rostedt Subject: Re: [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 In-Reply-To: References: <20120420122120.097464672@linutronix.de> <4F916AF3.7020301@linux.vnet.ibm.com> <871ume48ds.fsf@rustcorp.com.au> User-Agent: Notmuch/0.12 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Tue, 22 May 2012 10:23:47 +0930 Message-ID: <87mx512fz8.fsf@rustcorp.com.au> 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 On Mon, 21 May 2012 10:25:21 +0200 (CEST), Thomas Gleixner wrote: > On Mon, 21 May 2012, Rusty Russell wrote: > > > On Fri, 20 Apr 2012 16:18:04 +0200 (CEST), Thomas Gleixner wrote: > > > On Fri, 20 Apr 2012, Srivatsa S. Bhat wrote: > > > The whole notifier business needs a redesign as well, because we don't > > > have a way to express proper dependencies, we add random notifier > > > points and the teardown path is ass backwards. The whole thing wants > > > to be a tree which can be walked in either direction and from any > > > point. Right now we cut the trunk first and keep the single limb up > > > with a helicopter and start dismantling it. > > > > But there are two ways to do it. One is to eliminate the need for > > callbacks. The other is to make a full dependency-based callback > > What do you mean with fully eliminating the need for callbacks. Do you > want to put the necessary bringup/shutdown function calls just in the > core code so we get rid of the notifiers or do you have something > different in mind ? Eliminate is probably too hard, but with park/unpark I can see it getting less common. Maybe few enough that we can simplify. > > Not sure whether calling notifiers in parallel is going to be a big win: > > they'll end up fighting over the cpu we're taking down. But I could be > > wrong. > > I'm not going to aim for parallel in the first place. That was just an > idea and if we chose the right implementation then parallelism can be > added later. Parallel CPUs going offline/online is probably a bigger win. Both for suspend/resume and powersaving. > > The original concept of stopping the machine for cpu hotplug and trying > > not to effect any other kernel code has jumped the shark: I think we > > need to look seriously at a complete rewrite where we don't use > > stop_machine. > > Yep. Working on it. :) I thought you might be :) I'd love to review once you've got something. Cheers, Rusty.