[libvirt] About cgroup mechanism using in libvirt

[Daniel P. Berrange]

On Mon, Jun 14, 2010 at 03:28:42PM +0530, Balbir Singh wrote:
> On Mon, Jun 14, 2010 at 3:10 PM, Daniel P. Berrange <berrange at redhat.com> wrote:
> > On Sat, Jun 12, 2010 at 07:23:33AM -0400, Alex Jia wrote:
> >> Hey Daniel,
> >> The cgroup mechanism have been integrated into libvirt for LXC and QEMU driver,
> >> and the LXC driver uses all of cgroup controllers except for net_cls and cpuset,
> >> while the QEMU driver only uses the cpu and devices controllers at present.
> >>
> >> From the user point of view, user can use some virsh commands to control some
> >> guest resources:
> >> 1. Using 'virsh schedinfo' command to get/set CPU scheduler priority for a guest
> >
> > QEMU + LXC use the cpu controller 'cpu_shares' tunable
> >
> >> 2. Using 'virsh vcpuin' command to control guest vcpu affinity
> >
> > QEMU pins the process directly, doesn't use cgroups.  LXC has't
> > implemented this yet
> >
> >> 3. Using 'virsh setmem' command to change memory allocation
> >> 4. Using 'virsh setmaxmem' command to change maximum memory limit
> >
> > QEMU uses balloon driver.  LXC uses cgroups memory controller
> >
> 
> Not sure if I understand this, but the balloon driver and memory
> cgroups are not mutually exclusive. One could use both together and  I
> would certainly like to see additional commands to support cgroups.
> What happens if a guest (like freebsd) does not support ballooning?
> Are you suggesting we'll not need cgroups at all with QEMU?

No, I was merely describing the current usage. Making use of cgroups to
enforce the limit is certainly a desirable RFE for the future.

> >> 5. Using 'virsh setvcpus' command to change number of virtual CPUs
> >
> > QEMU uses cpu hotplug. LXC hasn't implemented this.
> >
> >> I just make sure the above 1 using CPU scheduler controller, maybe 4 using Memory
> >> controller? and maybe 5 using CPU set controller? I am not sure.
> >>
> 
> I think we'll some notion of soft limits as well, not sure if they can
> be encapsulated using the current set. We need memory shares for
> example to encapsulate them.


Daniel
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