Return-Path: <linux-kernel-owner+willy=40w.ods.org@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id <S267399AbTAMQSF>; Mon, 13 Jan 2003 11:18:05 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
	id <S267431AbTAMQSF>; Mon, 13 Jan 2003 11:18:05 -0500
Received: from ns.virtualhost.dk ([195.184.98.160]:39338 "EHLO virtualhost.dk")
	by vger.kernel.org with ESMTP id <S267399AbTAMQSE>;
	Mon, 13 Jan 2003 11:18:04 -0500
Date: Mon, 13 Jan 2003 17:26:38 +0100
From: Jens Axboe <axboe@suse.de>
To: Terje Eggestad <terje.eggestad@scali.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: any chance of 2.6.0-test*?
Message-ID: <20030113162638.GY14017@suse.de>
References: <Pine.LNX.4.44.0301121100380.14031-100000@home.transmeta.com> <1042400094.1208.26.camel@RobsPC.RobertWilkens.com> <1042400219.1208.29.camel@RobsPC.RobertWilkens.com> <20030112195347.GJ3515@louise.pinerecords.com> <1042401817.1209.54.camel@RobsPC.RobertWilkens.com> <1042472605.5404.72.camel@pc-16.office.scali.no> <20030113154954.GR14017@suse.de> <1042475145.5404.86.camel@pc-16.office.scali.no>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1042475145.5404.86.camel@pc-16.office.scali.no>
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Jan 13 2003, Terje Eggestad wrote:
> On man, 2003-01-13 at 16:49, Jens Axboe wrote:
> > On Mon, Jan 13 2003, Terje Eggestad wrote:
> > > Considering that doing kernel development is hard enough, new
> > > development is almost always done on uni processors kernels that do only
> > > one thing at the time. Then when you base logic is OK, you move to a
> > > SMP, which means (adding and) debugging you spin locks.
> > 
> > Goto's aside, I find the above extremely bad advise. You should _always_
> > develop with smp and for smp from the very start, or you will most
> > likely not get it right later on. With preempt, this becomes even more
> > important.
> 
> You should, and I do, *design* with smp in mind, and I throw in
> smplock/unlonk as I go, but I tend to make first runs on a UP. 
> 
> I see your point on preemt, though.
> You do first runs on SMP? 

Always, if for nothing else than the benefit of a better debugging
environment.

> > > Considering that fucking up spin locks are prone to corrupting your
> > > machine, one very simple trick to makeing fewer mistakes to to have one,
> > > and only one, unlock for every lock. 
> > 
> > Taking a spin lock twice will hard lock the machine, however on smp you
> > will typically have the luxury of an nmi watchdog which will help you
> > solve this quickly. Double unlock will oops immediately if you run with
> > spin lock debugging (you probably should, if you are developing kernel
> > code).
> 
> I have the console on a serial port, and a terminal server. With kdb,
> you can enter the kernel i kdb even when deadlocked.

Even if spinning with interrupt disabled?

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/