[systemd-devel] Fedora 25, cgroups V2 and systemd roadmap

Daniel P. Berrange berrange at redhat.com
Mon Oct 10 16:35:37 UTC 2016

On Mon, Oct 10, 2016 at 02:43:33PM +0200, Lennart Poettering wrote:
> On Mon, 10.10.16 14:31, Kevin Wilson (wkevils at gmail.com) wrote:
> > Hello, systemd developers,
> > So we have now 3 V2 cgroups controller in the kernel (pids, memory and io).
> > The CPU controller as of now is not merged in and is available only in
> > an out of tree git repo (due to some debate over
> > it with kernel scheduler developers). Not sure that it will be merged
> > in the next 2 months.
> > 
> > Fedora 25 is to be released in a month and a half, on 15 of November.
> > https://fedoraproject.org/wiki/Releases/25/Schedule
> > My questions are:
> > what are the intentions regarding using cgroup v2 in systemd  in F25
> > as the default instead of using cgroup V1?
> > Is the absence of  the CPU controller is a reason for not having
> > cgroup V2 as a default in F25 ? and if so, why ?
> I'd like to switch this over sooner rather than later in Fedora, but I
> figure we can't do that, unless relevant other upstreams can deal with
> the new hierarchy too. I figure on Fedora, that'd be at least libvirt
> and Docker that need to be updated for this.
> I figure we should start turning this on in Rawhide, and see what
> breaks, and then revert before the release.
> Before we can tell Docker/libvirt to port their stuff over I figure we
> also need one more addition in the systemd API for this: next to
> Delegate=yes|no (which we already have) we probably need to add
> DelegateController= taking a list of all controllers to
> delegate. Right now we delegate all controllers, but I figure that
> should be configurable, since turning on a controller might have
> effects people don't expect (in particular for the cpu hierarchy).

>From the libvirt POV, getting the CPU controller support merged is
a blocking item, otherwise we have a major feature regression. We
have a policy of not supporting code that is out of tree, as we don't
like getting burnt when changes are inevitably made after it is finally

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