On 2015/5/4 11:13, Mike Galbraith wrote:

On Mon, 2015-05-04 at 08:54 +0800, Zefan Li wrote:

quoted

It's allowed to promote a task from normal to realtime after it has been
attached to a non-root cgroup, but it will fail if the attaching happens
after it has become realtime. I don't see how this restriction is useful.

In the CONFIG_RT_GROUP_SCHED case, promotion will fail is there is no
bandwidth allocated.

Right. I forgot to mention this patch affects !CONFIG_RT_GROUP_SCHED only,
though it should be obvious by reading the change.

quoted

We are moving toward unified hierarchy where all the cgroup controllers
are bound together, so it would make cgroups easier to use if we have less
restrictions on attaching tasks between cgroups.

Forcing group scheduling overhead on users if they want cpuset or memory
cgroup functionality would be far from wonderful.  Am I interpreting the
implications of this unification/binding properly?

(I hope not, surely the plan is not to utterly _destroy_ cgroup utility)

Some degree of flexibility is provided so that you may disable some controllers
in a subtree. For example:

root                  ---> child1
(cpuset,memory,cpu)        (cpuset,memory)
                      \
                       \-> child2
                           (cpu)