Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946051AbXBPTC2 (ORCPT ); Fri, 16 Feb 2007 14:02:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1946050AbXBPTC1 (ORCPT ); Fri, 16 Feb 2007 14:02:27 -0500 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:37927 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946043AbXBPTC0 (ORCPT ); Fri, 16 Feb 2007 14:02:26 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Jeremy Fitzhardinge Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Andi Kleen , Benjamin Herrenschmidt , Ingo Molnar , Alan Cox Subject: Re: [RFC] killing the NR_IRQS arrays. References: <45D5F2EC.5000402@goop.org> Date: Fri, 16 Feb 2007 12:01:43 -0700 In-Reply-To: <45D5F2EC.5000402@goop.org> (Jeremy Fitzhardinge's message of "Fri, 16 Feb 2007 10:07:40 -0800") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1504 Lines: 31 Jeremy Fitzhardinge writes: > Eric W. Biederman wrote: >> So I propose we remove all assumptions from the code that we actually >> have an array of irqs. That will allow for irq_desc to be dynamically >> allocated instead of statically allocated saving memory and reducing >> kernel complexity. >> > > Sounds good to me. In Xen we have 1024 event channels which we need to > map down into a smaller irq. Aside from the complexity of maintaining a > mapping table, that's not a huge issue for now, but when we start > exposing pci devices to guests it all becomes more complex. The ideal > for us is to simply use event channel == irq, which this would allow. Well you shouldn't need to wait just run with a kernel with NR_IRQS >= 1024. 1024 is stretch but it isn't to bad. There are already x86 boxes that have more pins on their ioapics then that. So x86_64 and with this latest round of patches from Len Brown and I i386 should be able to support that. On the other side 1024 looks extremely limiting for exposing pci devices. If someone gets serious about pushing what is legal with MSI-X you may be in trouble. As a single device is allowed to have 4096 interrupts. Not that I can think of a user for so many but... Eric - 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/