On Mon, Mar 10, 2014 at 03:47:49PM +0100, Jiri Denemark wrote: > On Mon, Mar 10, 2014 at 15:36:06 +0100, Olaf Hering wrote: > > > > During live migration of VMs from one host to another the VM is > > suspended for an unpredictable amount of time. The actual downtime > > depends on how many new pages will be dirty and the band width to the > > destination host. Since VM memory size grows faster than transfer rates > > the currently available tuneables will cause troubles for workloads > > within the VM which can not handle large timejumps. > > > > I have already written code to tweak the inner loop doing the actual > > migration work in libxc. But the patchset exposes the details of the > > loop to the cmdline, as such it is not portable nor is it a friendly UI > > for the hostadmin. > > > > > > Here is my proposal for a new option for virsh and 2 new options for xl: > > > > [xl | virsh --live] --max-suspend-time N --timeout N VM host > > > > --max-suspend-time N: as the name suggests, the VM downtime must not be > > longer than specified. The code doing the migration has to estimate the > > transfer speed. If the VM is about to be suspended, it has to check if > > the remaining dirty pages can be transfered within the required > > timeframe. If not, the migration is aborted, the VM continues to run on > > the src host, the new VM on the dst host is destroyed and an error is > > returned. > > Libvirt already has virDomainMigrateSetMaxDowntime API with this > semantics. However, using virsh, one can set it with virsh > migrate-setmaxdowntime command while migration is happening. Not sure if > exposing it as yet another parameter of already quite complicated > migrate command would buy us much. I think it is valuable to have it as a parameter to 'migrate' - since 'migrate' blocks, you'd have to open up a second shell to set the downtime which is kind of tedious. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list