On Thu, Jun 11, 2015 at 01:50:24PM +0300, Andrey Korolyov wrote:
Hi Daniel,
would it possible to adopt an optional tunable for a virCgroup mechanism which targets to a disablement of a nested (per-thread) cgroup creation? Those are bringing visible overhead for many-threaded guest workloads, almost 5% in non-congested host CPU state, primarily because the host scheduler should make a much more decisions with those cgroups than without them. We also experienced a lot of host lockups with currently exploited cgroup placement and disabled nested behavior a couple of years ago. Though the current patch is simply carves out the mentioned behavior, leaving only top-level per-machine cgroups, it can serve for an upstream after some adaptation, that`s why I`m asking about a chance of its acceptance. This message is a kind of 'request of a feature', it either can be accepted/dropped from our side or someone may give a hand and redo it from scratch. The detailed benchmarks are related to a host 3.10.y, if anyone is interested in the numbers for latest stable, I can update those.
When you say nested cgroup creation, as you referring to the modern libvirt hierarchy, or the legacy hierarchy - as described here: http://libvirt.org/cgroups.html The current libvirt setup used for a year or so now is much shallower than previously, to the extent that we'd consider performance problems with it to be the job of the kernel to fix. 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 :|