Re: [libvirt] Overhead for a default cpu cg placement scheme

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 --