From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756734Ab1I3QJo (ORCPT ); Fri, 30 Sep 2011 12:09:44 -0400 Received: from claw.goop.org ([74.207.240.146]:45553 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752511Ab1I3QJm (ORCPT ); Fri, 30 Sep 2011 12:09:42 -0400 Message-ID: <4E85E9C4.1090606@goop.org> Date: Fri, 30 Sep 2011 09:09:40 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2 MIME-Version: 1.0 To: Steven Rostedt CC: "David S. Miller" , David Daney , Michael Ellerman , Jan Glauber , Jason Baron , the arch/x86 maintainers , Xen Devel , Linux Kernel Mailing List , Jeremy Fitzhardinge Subject: Re: [PATCH RFC 0/8] jump-label: allow early jump_label_enable() References: <1317343975.4588.36.camel@gandalf.stny.rr.com> <4E854859.4020105@goop.org> <1317396484.4588.52.camel@gandalf.stny.rr.com> In-Reply-To: <1317396484.4588.52.camel@gandalf.stny.rr.com> X-Enigmail-Version: 1.3.2 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/30/2011 08:28 AM, Steven Rostedt wrote: > On Thu, 2011-09-29 at 21:40 -0700, Jeremy Fitzhardinge wrote: >> On 09/29/2011 05:52 PM, Steven Rostedt wrote: >>> On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote: >>>> From: Jeremy Fitzhardinge >>>> >>>> One big question which arises is whether the _early() function is >>>> necessary at all. All the stop_machine/mutex/etc stuff that >>>> arch_jump_label_transform() ends up doing is redundant pre-SMP, but it >>>> shouldn't hurt. Maybe we can just drop the _early function? It works >>>> on x86, at least, because jump_label_enable() works, which uses the full >>>> form. And dropping it would reduce this to a very much smaller series. >>> It does slow down the boot process, which is not a good thing when >>> everyone is pushing for the fastest restarts. >> Would it really though? stop_machine() doesn't do very much when there >> are no other cpus. >> >> Not that I measured or anything, but there was no obvious big lag at boot. > Just bringing up the point, but without measurements, its all hand > waving. It may not be a big deal, and simpler code is always better if > it doesn't harm anything else. I think the simplest thing is to make stop_machine() well-defined in a pre-smp environment, where it just directly calls the callback: diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index ba5070c..b6ad9b3 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -485,6 +485,11 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) .num_threads = num_online_cpus(), .active_cpus = cpus }; + if (smdata.num_threads == 1) { + (*fn)(data); + return 0; + } + /* Set the initial state and stop all online cpus. */ set_state(&smdata, STOPMACHINE_PREPARE); return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); so that its guaranteed safe to use at any point. J