From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39215) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1chDTO-0005DR-50 for qemu-devel@nongnu.org; Fri, 24 Feb 2017 05:51:39 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1chDTN-0007lY-2J for qemu-devel@nongnu.org; Fri, 24 Feb 2017 05:51:38 -0500 References: <148776029578.5865.5785337570950575739.stgit@bahia> From: Thomas Huth Message-ID: Date: Fri, 24 Feb 2017 11:51:33 +0100 MIME-Version: 1.0 In-Reply-To: <148776029578.5865.5785337570950575739.stgit@bahia> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] spapr/pci: populate PCI DT in reverse order List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz , qemu-devel@nongnu.org, David Gibson Cc: Nikunj A Dadhania , "Michael S. Tsirkin" , qemu-ppc@nongnu.org, Marcel Apfelbaum On 22.02.2017 11:56, Greg Kurz wrote: > From: Greg Kurz [...] > This patch reverts to the historical SLOF ordering by walking PCI devices > in reverse order. This reconciles pseries with x86 machine types behavior. > It is expected to make things easier when porting existing applications to > power. [...] > This patch was posted and already discussed during 2.5 development: > > http://patchwork.ozlabs.org/patch/549925/ > > The "consensus" at the time was that guests should not rely on device > ordering (i.e. use persistent naming instead). > > I got recently contacted by OpenStack people who had several complaints > about the reverse ordering of PCI devices in pseries: different behavior > between ppc64 and x86, lots of time spent in debugging when porting > applications from x86 to ppc64 before realizing that it is caused by the > reverse ordering, necessity to carry hacky workarounds... > > One strong argument against handling this properly with persistent naming > is that it requires systemd/udev. This option is considered as painful > with CirrOS, which aims at remaining as minimal as possible and is widely > used in the OpenStack ecosystem. > > Would you re-consider your position and apply this patch ? +1 for applying the patch. During the past months, I've also run one or two times into issues with the reversed ordering... fortunately, I was able to work around them (or fix other bugs triggered by this), but I think it would be better to return the the ascending order again to avoid further future problems. Thomas