On Sun, Oct 29, 2017 at 05:36:53PM +0100, Maciej S. Szmigiero wrote: > CFQ scheduler has a property that processes (or tasks in cgroups v1) that > aren't assigned to any particular cgroup - that is, which stay in the root > cgroup - effectively form an implicit leaf child node attached to the root > cgroup. > > This behavior is documented in blkio-controller.txt for cgroups v1, however > as far as I know it isn't documented anywhere for cgroups v2 besides a > generic remark that "How resource consumption in the root cgroup is > governed is up to each controller" in cgroup-v2.txt. > > By default, this implicit leaf child node has a (CFQ) weight which is two > times higher that the default weight of a child cgroup. > > cgroups v1 provide a "leaf_weight" setting which allow changing this value. > However, this setting is missing from cgroups v2 and so the only way to > tweak how much IO time processes in the root cgroup get is to adapt > weight settings of all child cgroups accordingly. > Let's add a "leaf_weight" setting to the root cgroup in cgroups v2, too. > > Note that new kernel threads appear in the root cgroup and there seems to > be no way to change this since kthreadd cannot be moved to another cgroup > (for a good reason). > > Signed-off-by: Maciej S. Szmigiero <mail@xxxxxxxxxxxxxxxxxxxxx> I don't think we wanna do this. It's inconsistent with what other controllers do and we want to charge the IOs in the root cgroup to the right cgroup. Thanks. -- tejun
