From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753196AbXLEWsJ (ORCPT ); Wed, 5 Dec 2007 17:48:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752707AbXLEWr5 (ORCPT ); Wed, 5 Dec 2007 17:47:57 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:43641 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752671AbXLEWr4 (ORCPT ); Wed, 5 Dec 2007 17:47:56 -0500 Date: Wed, 5 Dec 2007 14:47:23 -0800 From: Gary Hade To: "Jun'ichi Nomura" Cc: Gary Hade , linux-kernel@vger.kernel.org, linux-pci@atrey.karlin.mff.cuni.cz, Greg KH , jbeulich@novell.com Subject: Re: [PATCH] pci: Omit error message for benign allocation failure Message-ID: <20071205224723.GC5964@us.ibm.com> References: <4755AC14.20605@ce.jp.nec.com> <20071204214907.GB9194@us.ibm.com> <4755E174.7040106@ce.jp.nec.com> <20071205014506.GA6034@us.ibm.com> <4756C140.6040601@ce.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4756C140.6040601@ce.jp.nec.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 05, 2007 at 10:18:24AM -0500, Jun'ichi Nomura wrote: > Gary Hade wrote: > > On Tue, Dec 04, 2007 at 06:23:32PM -0500, Jun'ichi Nomura wrote: > >> Kernel always tries to. But it's best effort basis, IMO. > >> (Maybe your patch is going to fix that?) > > > > If you are seeing the allocation failures both with and > > without my original patch I doubt that an improved version > > would work. In my case, the BIOS had allowed sufficient > > resource for the expansion ROMs but was expecting the kernel > > to get it from the non-prefetch instead of prefetch window. > > OK. Then it's different from mine. > Thanks for the info. No problem. Since our goals (eliminate confusing PCI memory allocation failure messages) are the same and since your patch would partially (see below) fix the issue that my patch was attempting to address, I am _very_ interested to see how others who are more expansion ROM knowledgeable than myself react to your proposal. In fact, if what you are saying is correct, I'm wondering why the kernel even needs to attempt (by default) to obtain space for expansion ROMS that on some systems could be better utilized elsewhere. Perhaps the default behavior could be changed to exclude the expansion ROM allocation attempts with a new kernel option added to enable the current behavior for those that might want it. I think this would solve both of our problems. I will now bore you with my story and how it relates to your change. The issue that my patch was attempting to address involves a PCIe adapter that contains a p2p bridge above a SCSI storage controller: [root@elm3a9 ~]# lspci -s 0b:00.0 0b:00.0 PCI bridge: PLX Technology, Inc. PEX 8114 PCI Express-to-PCI/PCI-X Bridge (rev bc) [root@elm3a9 ~]# lspci -ts 0b:00.0 -+-[0000:0b]---00.0-[0000:0c]-- \-[0000:00]- [root@elm3a9 ~]# lspci -s 0c:04.0 0c:04.0 SCSI storage controller: Adaptec ASC-29320ALP U320 (rev 10) Case 1: (non-hotplug) Without my patch and in non-hotplug context (adapter installed at boot time) we see an allocation failure for the prefetch window that was created due to the BIOS unassigned expansion ROM BAR on the SCSI controller: PCI: Failed to allocate mem resource #9:100000@f2800000 for 0000:0b:00.0 This is happening because the BIOS allowed space in the non-prefetch window for the expansion ROM and provided no extra space for the unexpected kernel created prefetch window. Case 2: (hotplug) Without my patch and in hotplug context (same adapter hotplugged to the same slot that it was in at boot time) we see an allocation failure for BAR 0 of the bridge: PCI: Failed to allocate mem resource #0:2000@f2800000 for 0000:0b:00.0 This is happening because allocations for both the non-prefetch window and expansion ROM motivated prefetch window succeeded consuming all of the memory that the BIOS had provided for the adapter. This left no memory for bridge BAR 0. Your patch eliminates Case 1 by hiding the prefetch window allocation failure. Case 2 is unfortunately still alive and well because the expansion ROM motivated prefetch window is still consuming the memory that the BIOS provided for bridge BAR 0. After seeing Jan's report it became obvious that expansion ROMs cannot always be directed to a single type (prefetch or non-prefetch) of window. I know of no direct way of determining where the BIOS expects expansion ROMs to land so some sort of intelligent choice based on other information needs to be made. This is what I have been struggling with. I can handle a simple case where expansion ROM(s) are directed to the non-prefetch window if the calculated non-prefetch window size both with and without expansion ROM(s) is the same. I haven't yet figured out how to handle cases where the with/without expansion ROM non-prefetch window sizes differ. In these cases the BIOS's intention does not appear to be clear. This is why I really like the "skip the default expansion ROM allocation attempts" idea that your proposal has spawned. :) Thanks for your excellent idea. Gary -- Gary Hade System x Enablement IBM Linux Technology Center 503-578-4503 IBM T/L: 775-4503 garyhade@us.ibm.com http://www.ibm.com/linux/ltc