On 03/21/2014 01:00 PM, Serge E. Hallyn wrote: > Quoting Cole Robinson (crobi...@redhat.com): >> On 03/19/2014 12:16 PM, Serge E. Hallyn wrote: >>> Quoting Serge E. Hallyn (se...@hallyn.com): >>>> Quoting Paolo Bonzini (pbonz...@redhat.com): >>>>> Il 19/03/2014 16:42, Serge E. Hallyn ha scritto: >>>>>> Hi, >>>>>> >>>>>> at https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1291321 >>>>>> it was found that migrating running vms from a machine with >>>>>> qemu-kvm to one with qemu, migration fails due to some mismatches. >>>>>> The first one we usually hit is >>>>>> >>>>>> Length mismatch: vga.vram: 1000000 in != 800000 >>>>>> >>>>>> while the second one is network card (and I have not gone beyond >>>>>> that). >>>>> >>>>> This is just a different default. Make sure you specify the right >>>>> model on the command line. >>>>> >>>>>> The vga one can be handled on the command line by >>>>>> specifying the -global cirrus-vga.vrammem_mb=8. However that >>>>>> doesn't help with a libvirt migration. >>>>> >>>>> You can patch Ubuntu's QEMU to detect old machine types (pc-1.2 and >>>>> earlier) and give cirrus-vga 16MB memory by default. Migration only >>>>> works with versioned machine types (or between same-version QEMU), >>>>> so it's okay to only do it there. >>>>> >>>>>> I guess this happens at ram_load() unfortunately - is there any >>>>>> good way that this could be detected at incoming migration time >>>>>> and the virtual hardware modified as needed for migration to >>>>>> continue? >>>>> >>>>> It cannot, but the destination can be patched to operate correctly >>>>> for the old machine types, on the assumption that migration from the >>>>> old machine types is always from Ubuntu's qemu-kvm. >>>>> >>>>> Paolo >>>> >>>> Ah, thank you, that assumption should be safe and sounds like a >>>> great idea. >>> >>> Although, some people are using newer qemu with '-M pc-1.0'. So we'd be >>> stopping thing from migrating to support the people coming from qemu-kvm. >>> Hmm. >>> >> >> FWIW, we've carried a patch like this in Fedora 18, 19, and 20: >> >> http://pkgs.fedoraproject.org/cgit/qemu.git/tree/0001-Fix-migration-from-qemu-kvm.patch?h=f20 >> >> As you say, it breaks incoming migration from stock qemu.git. But we never >> shipped qemu.git prior to F18 (well, not in any timeframe that matters here), >> so back compat wasn't a real concern. >> >> For Fedora 21 we are dropping this patch, since there's been enough releases >> for the people to transition: >> >> http://blog.wikichoon.com/2013/12/kvm-migration-from-fedora-17-to-fedora.html > > Thanks, Cole. I notice it doesn't do anything for -vga cirrus - is that > just bc in general fedora users tend to use -vga qxl? >
Line 149 of the patch changes the cirrus-vga default memory for old machine types, seems to fix things in my testing. - Cole
