Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760247AbZANW44 (ORCPT ); Wed, 14 Jan 2009 17:56:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754729AbZANW4q (ORCPT ); Wed, 14 Jan 2009 17:56:46 -0500 Received: from mx2.redhat.com ([66.187.237.31]:45455 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754570AbZANW4p (ORCPT ); Wed, 14 Jan 2009 17:56:45 -0500 Subject: Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot interrupt equivalent From: Jon Masters To: "Eric W. Biederman" Cc: Ingo Molnar , Bjorn Helgaas , Stefan Assmann , Len Brown , Jesse Barnes , Olaf Dabrunz , Thomas Gleixner , Steven Rostedt , Linux Kernel Mailing List , linux-acpi@vger.kernel.org, Sven Dietrich , "Maciej W. Rozycki" In-Reply-To: References: <496B24E5.1070804@suse.de> <200901121151.53195.bjorn.helgaas@hp.com> <1231806563.4094.25.camel@perihelion.bos.jonmasters.org> <20090113014723.GA11366@elte.hu> <1231820798.4094.34.camel@perihelion.bos.jonmasters.org> <20090114114006.GF8625@elte.hu> <1231960709.23174.0.camel@londonpacket.bos.redhat.com> Content-Type: text/plain Organization: Red Hat, Inc. Date: Wed, 14 Jan 2009 17:56:00 -0500 Message-Id: <1231973760.23174.33.camel@londonpacket.bos.redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2070 Lines: 52 On Wed, 2009-01-14 at 14:42 -0800, Eric W. Biederman wrote: > Jon Masters writes: > > > On Wed, 2009-01-14 at 12:40 +0100, Ingo Molnar wrote: > > > >> it's not just -rt, but it is also needed for the concept of threaded IRQ > >> handlers - which was discussed at the Kernel Summit to be desired for > >> mainline. > > > > Right. I'm poking at Thomas' patches and hope to post something soon on > > that front - I'm acutely aware that this will be impacted aswell but > > because it's vaguely RT related had banded it under that banner. > > Stepping back a moment. The only way I can see this working reliably > is if we disable the boot interrupt. Anything that leaves the boot interrupt > enabled means that when we disable the primary interrupt the boot interrupt > will scream, and thus we must disable it as well. > > Which leads to my problem with the entire development process of this feature. > > People want the feature. > People don't want to pay attention to the limits of the hardware. > Which leads to countless broken patches proposed. Is a patch broken because hardware has limitations? If that were always true then many of the patches we see in the kernel wouldn't be there. > Which leads me to conclude. > - IRQ handling in the RT kernel is hopelessly broken. Nope. It's done in a very similar way to other real time kernels already out there - really there are only so many ways to do this. > - IRQ threads are a bad idea. Why? IRQ threads actually make life so much easier - you have a task context, you can do everything inside that rather than scheduling all kinds of deferred work (that in RT will be done in another task later), and so forth. > None of this works reliably on level triggered ioapic irqs. Level triggered IOAPIC IRQs have quirks, film at 11! Jon. -- 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/