[libvirt] About cgroup mechanism using in libvirt

[Balbir Singh]

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?

>> 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.

Balbir