Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755169AbYGMXcV (ORCPT ); Sun, 13 Jul 2008 19:32:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754274AbYGMXcL (ORCPT ); Sun, 13 Jul 2008 19:32:11 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:48006 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752536AbYGMXcJ (ORCPT ); Sun, 13 Jul 2008 19:32:09 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: benh@kernel.crashing.org Cc: Suresh Siddha , Matthew Wilcox , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "grundler@parisc-linux.org" , "mingo@elte.hu" , "tglx@linutronix.de" , "jgarzik@pobox.com" , "linux-ide@vger.kernel.org" , "jbarnes@virtuousgeek.org" , "rdunlap@xenotime.net" , "mtk.manpages@gmail.com" References: <20080711005719.GO14894@parisc-linux.org> <20080711215943.GW1678@linux-os.sc.intel.com> <1215834720.7549.154.camel@pasglop> <1215848161.7549.166.camel@pasglop> <1215989044.7549.219.camel@pasglop> Date: Sun, 13 Jul 2008 16:29:45 -0700 In-Reply-To: <1215989044.7549.219.camel@pasglop> (Benjamin Herrenschmidt's message of "Mon, 14 Jul 2008 08:44:04 +1000") 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 X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;benh@kernel.crashing.org X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * 0.0 BAYES_50 BODY: Bayesian spam probability is 40 to 60% * [score: 0.4391] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral Subject: Re: Multiple MSI, take 3 X-SA-Exim-Version: 4.2 (built Thu, 03 Mar 2005 10:44:12 +0100) X-SA-Exim-Scanned: Yes (on mgr1.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1370 Lines: 33 Ben. Multi-MSI is a crap hardware design. Why do you think we have MSI-X? MSI-X as specced is a properly operating irq controller that we don't need kludges to support. Multi-MSI with a full set of kludges almost work but not quite fits the linux irq model. Any hardware designer who choose to implement Multi-MSI instead of MSI-X was not really concerned about having a high performance device. If we can find a way to model the portable capabilities of Multi-MSI cleanly then we can support it, and our drivers and our users and our intermediate layers won't get surprised. So far we have too close fits but neither model really works. Further this is all about driver optimization, so none of this is necessary to have working hardware. Which makes kludges much less appropriate. Modelling Multi-MSI irqs as normal irqs requires a lot of nasty kludges. One of the kludges is allocating a continuous chunk of irq targets, and the resulting fragmentation issues that you get when you start allowing different sized allocations. Overall if Multi-MSI was to become common I think we would really regret it. 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/