From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37032) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WYcv5-00074H-El for qemu-devel@nongnu.org; Fri, 11 Apr 2014 10:59:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WYcuz-0007DX-4r for qemu-devel@nongnu.org; Fri, 11 Apr 2014 10:59:07 -0400 Message-ID: <53480331.1080106@suse.de> Date: Fri, 11 Apr 2014 16:58:57 +0200 From: Alexander Graf 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> <5347E263.7050605@ozlabs.ru> <53480131.4070203@ozlabs.ru> In-Reply-To: <53480131.4070203@ozlabs.ru> Content-Type: text/plain; charset=UTF-8; format=flowed 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: Alexey Kardashevskiy Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, =?UTF-8?B?QW5kcmVhcyBGw6Ry?= =?UTF-8?B?YmVy?= On 11.04.14 16:50, Alexey Kardashevskiy wrote: > On 04/11/2014 11:58 PM, Alexander Graf wrote: >> On 11.04.2014, at 14:38, Alexey Kardashevskiy wrote: >> >>> 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. >> Ok, let me rephrase. If I shut the machine down because I'm doing >> on-disk hibernate and then boot it back up, will the guest find the same >> configuration? > > I do not understand what you mean by this. Hibernation by the guest OS > itself or by QEMU? If this involves QEMU exit and QEMU start - then yes, by the guest OS. The host will only see a genuine "shutdown" event. The guest OS will expect the machine to look *the exact same* as before the shutdown. > config may be different. If it is "migrate to file" and then "migrate from > file" (do not know what you call it when migration goes to a pipe which is > "tar") - then config will be the same. > > >>>> 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? :) >> The better solution wins :) > We both know who decides ;) I posted series, I need heads up if it is going > the right way or not. It's not :). If a guest may not have different IRQ allocation after migration, it also must not have different IRQ allocation after shutdown + restart. Alex