From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266565AbUGKLOu (ORCPT ); Sun, 11 Jul 2004 07:14:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266568AbUGKLOu (ORCPT ); Sun, 11 Jul 2004 07:14:50 -0400 Received: from fw.osdl.org ([65.172.181.6]:6806 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S266565AbUGKLOq (ORCPT ); Sun, 11 Jul 2004 07:14:46 -0400 Date: Sun, 11 Jul 2004 04:13:29 -0700 From: Andrew Morton To: Arjan van de Ven Cc: mingo@elte.hu, linux-kernel@vger.kernel.org, linux-audio-dev@music.columbia.edu Subject: Re: [announce] [patch] Voluntary Kernel Preemption Patch Message-Id: <20040711041329.22f637d1.akpm@osdl.org> In-Reply-To: <20040711105936.GA13956@devserv.devel.redhat.com> References: <20040709182638.GA11310@elte.hu> <20040710222510.0593f4a4.akpm@osdl.org> <20040711093209.GA17095@elte.hu> <20040711024518.7fd508e0.akpm@osdl.org> <20040711095039.GA22391@elte.hu> <20040711025855.08afbca1.akpm@osdl.org> <20040711103020.GA24797@elte.hu> <20040711034258.796f8c6a.akpm@osdl.org> <20040711105936.GA13956@devserv.devel.redhat.com> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: > > On Sun, Jul 11, 2004 at 03:42:58AM -0700, Andrew Morton wrote: > > > We do not want to enable preempt for Fedora yet because it > > > breaks just too much stuff > > > > What stuff? > > just look over all the "fix preempt" stuff that got added to the kernel in > the last 6 months. Sometimes subtle sometimes less so. From a distribution > POV I don't want a potential slew of basically impossible to reproduce > problems, especially this young in 2.6, there are plenty of other problems > already (and before you ask "which", just look at how many bugs got fixed in > the last X weeks for any value of X, and look at say acpi issues). > Yes I understand this puts you into a bit of a bad position, several distros > not enabling preempt means that it gets less testing than it should. > However.. there's only so much issues distros can take and with 2.6 still > quite fresh... > IOW: "we haven't found any such stuff". Sounds fuddy to me. > > > (Long-term i'd like to see preempt be used unconditionally - at which > > > point the 10-line CONFIG_VOLUNTARY_PREEMPT Kconfig and kernel.h change > > > could go away.) > > > > And "stuff" is already broken on SMP, yes? > > That's the classic preempt "myth"; it's true if you ignore per cpu stuff and > some other subtle issues ;) ? Sticking a WARN_ON(!in_atomic()) if CONFIG_PREEMPT into smp_processor_id() should catch any missed fixes. > And even then, yes a lot of our drivers are not > quite SMP safe. Take ISDN or any of the other declared SMP-broken drivers. > Not to speak of the ones that aren't declared as such yet still are. > Regardless of Hyperthreading, smp is still quite rare while crappy > hardware/drivers are not. > Oh I can buy the make-the-bugs-less-probable practical argument, but sheesh. If you insist on going this way we can stick the patch in after 2.7 has forked. I spose. The patch will actually slow the rate of improvement of the kernel :(