On Mon, Nov 07, 2016 at 10:34:39PM +0200, Vlad Nykytiuk wrote: > Hi, > > As you may know, currently QEMU supports several features that help live > migrations to operate more predictively. These features are: auto-converge > and post-copy. > I made a research on performance characteristics of these two features, you > can find it by the following link: > https://rk4n.github.io/2016/08/10/qemu-post-copy-and-auto-converge-features/ > <https://rk4n.github.io/2016/08/10/qemu-post-copy-and-auto-converge-features/>
Thanks for the report, it looks to affirm the results that I've got previously that show post-copy as the clear winner, and auto-converge a viable alternative if post-copy is not available. I've got a few suggestions if you want to do further investigation - Look at larger guests - a 1 vCPU guest with 2 GB of RAM is not particularly difficult to migrate when you have 10 Gig-E networking or even 1 Gig-E networking. 4 vCPU with 8 GB of RAM, with 4 guest workers dirtying all 8 GB of RAM is a hard test. Even with autoconverge such guests may not successfully complete in < 5 minutes. - Measure the guest CPU performance eg time to write to 1 GB of RAM While auto-converge can ensure completion, it has a really high and prolonged impact on guest CPU performance, much worse than is seen with post-copy. For example, time to write to 1 GB will degrade from 400 ms/GB, to as much as 7000 ms/GB during post-copy, and this hit may last many minutes. For post-copy, there will be small spikes at the start of each iteration of migration ( 400ms/GB -> 1000ms/GB), and a big spike at the switch over (400ms/GB -> 7000ms/GB), but the duration of the spikes is very short (less than a second), so is a clear winner over auto-converge where the guest CPU performance hit lasts many minutes. - Measure the overall CPU utilization of QEMU as a whole. This will show impact of using compression, which is is to burn massive amounts of CPU time in the QEMU migration thread I've published by previous results here: https://www.berrange.com/posts/2016/05/12/analysis-of-techniques-for-ensuring-migration-completion-with-kvm/ and the framework I used to collect all this data is distributed in QEMU git repo now. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :| __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: [email protected]?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
