From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34005) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WYajh-0003Pn-To for qemu-devel@nongnu.org; Fri, 11 Apr 2014 08:39:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WYajZ-0000yC-6B for qemu-devel@nongnu.org; Fri, 11 Apr 2014 08:39:13 -0400 Received: from mail-pd0-f179.google.com ([209.85.192.179]:48290) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WYajY-0000xo-UQ for qemu-devel@nongnu.org; Fri, 11 Apr 2014 08:39:05 -0400 Received: by mail-pd0-f179.google.com with SMTP id w10so5270417pde.10 for ; Fri, 11 Apr 2014 05:39:04 -0700 (PDT) Message-ID: <5347E263.7050605@ozlabs.ru> Date: Fri, 11 Apr 2014 22:38:59 +1000 From: Alexey Kardashevskiy MIME-Version: 1.0 References: <1394770689-29039-1-git-send-email-aik@ozlabs.ru> <1394770689-29039-7-git-send-email-aik@ozlabs.ru> <534693E4.1050204@suse.de> <53469B86.7020400@ozlabs.ru> <53469BF3.7000406@suse.de> <5346AE11.1050206@ozlabs.ru> <5347B4D3.9060508@suse.de> In-Reply-To: <5347B4D3.9060508@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 6/8] spapr: move interrupt allocator to xics List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf , qemu-devel@nongnu.org Cc: qemu-ppc@nongnu.org, =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= On 04/11/2014 07:24 PM, Alexander Graf wrote: > > On 10.04.14 16:43, Alexey Kardashevskiy wrote: >> On 04/10/2014 11:26 PM, Alexander Graf wrote: >>> On 10.04.14 15:24, Alexey Kardashevskiy wrote: >>>> On 04/10/2014 10:51 PM, Alexander Graf wrote: >>>>> On 14.03.14 05:18, Alexey Kardashevskiy wrote: >>>>>> The current allocator returns IRQ numbers from a pool and does not >>>>>> support IRQs reuse in any form as it did not keep track of what it >>>>>> previously returned, it only had the last returned IRQ. >>>>>> However migration may change interrupts for devices depending on >>>>>> their order in the command line. >>>>> Wtf? Nonono, this sounds very bogus and wrong. Migration shouldn't change >>>>> anything. >>>> I put wrong commit message. By change I meant that the default state >>>> before >>>> the destination guest started accepting migration is different from what >>>> the destination guest became after migration finished. And migration >>>> cannot >>>> avoid changing this default state. >>> Ok, why is the IRQ configuration different? >> Because QEMU creates devices in the order as in the command line, and >> libvirt changes this order - the XML used to create the guest and the XML >> which is sends during migration are different. libvirt thinks it is ok >> while it keeps @reg property for (for example) spapr-vscsi devices but it >> is not because since the order is different, devices call IRQ allocator in >> different order and get different IRQs. > > So your patch migrates the current IRQ configuration, but once you restart > the virtual machine on the destination host it will have different IRQ > numbering again, right? No, why? IRQs are assigned at init time from realize() callbacks (and survive reset) or as a part of ibm,change-msi rtas call which happens in the same order as it only depends on pci addresses and we do not change this either. > I'm not sure that's a good solution to the problem. I guess we should > rather aim to make sure that we can make IRQ allocation explicit. > Fundamentally the problem sounds very similar to the PCI slot allocation > which eventually got solved by libvirt specifying the slots manually. We can do that too. Who decides? :) -- Alexey