From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH][PCI]: Introduce pci_find_capability_cached and make MSI use it Date: Fri, 16 May 2008 15:33:56 -0300 Message-ID: <20080516183356.GA7307@ghostprotocols.net> References: <20080515160426.GD14846@ghostprotocols.net> <20080515170407.GM9921@parisc-linux.org> <20080515171003.GF14846@ghostprotocols.net> <200805161044.34938.jbarnes@virtuousgeek.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Arnaldo Carvalho de Melo , Matthew Wilcox , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-rt-users@vger.kernel.org To: Jesse Barnes Return-path: Received: from mx1.redhat.com ([66.187.233.31]:36211 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751409AbYEPSeB (ORCPT ); Fri, 16 May 2008 14:34:01 -0400 Content-Disposition: inline In-Reply-To: <200805161044.34938.jbarnes@virtuousgeek.org> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Em Fri, May 16, 2008 at 10:44:34AM -0700, Jesse Barnes escreveu: > On Thursday, May 15, 2008 10:10 am Arnaldo Carvalho de Melo wrote: > > Em Thu, May 15, 2008 at 11:04:07AM -0600, Matthew Wilcox escreveu: > > > On Thu, May 15, 2008 at 01:04:26PM -0300, Arnaldo Carvalho de Melo wrote: > > > > So I implemented pci_find_capability_cached and made MSI use it > > > > for good measure, please consider applying. > > > > > > As I told you on IRC, this is just the MSI code being complete crap. > > > It should be caching the offset itself. We shouldn't have this extra > > > array in the struct pci_dev just because MSI is broken. > > > > Well, we can certainly do that, its just that I did this first and > > thought that perhaps there could be some other users, but I see that 44 > > extra bytes per pci_dev can be a pain if the only one to reap benefits > > is MSI, can't you think of any other users? I couldn't detect any so far > > in my admitedly limited testing. > > There are a few other common cap checks, but I don't think they compare to MSI > in terms of latency sensitivity (though I didn't audit all the CAP_ID_EXP > checks, there are quite a few of those). > > Since we know MSI is a problem, let's just go with fixing that for now. If we > find that other caps are also causing problems we can revisit caching all of > them; the patch is simple enough. Do you want me to submit another patch or can you cook up one? - Arnaldo