[systemd-devel] [HEADSUP] cgroup changes

[Daniel P. Berrange]

On Mon, Jun 24, 2013 at 03:27:15PM +0200, Lennart Poettering wrote:
> On Sat, 22.06.13 15:19, Andy Lutomirski (luto at amacapital.net) wrote:
> 
> > 1. I put all the entire world into a separate, highly constrained
> > cgroup.  My real-time code runs outside that cgroup.  This seems to
> > exactly what slices are for, but I need kernel threads to go in to
> > the constrained cgroup.  Will systemd support this?
> 
> I am not sure whether the ability to move kernel threads into cgroups
> will stay around at all, from the kernel side. Tejun, can you comment
> on this?

KVM uses the vhost_net device for accelerating guest network I/O
paths. This device creates a new kernel thread on each open(),
and that kernel thread is attached to the cgroup associated
with the process that open()d the device.

If systemd allows for a process to be moved between cgroups, then
it must also be capable of moving any associated kernel threads to
the new cgroup at the same time. This co-placement of vhost-net
threads with the KVM process, is very critical for I/O performance
of KVM networking.

Regards,
Daniel
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