On Thu, Jan 31, 2008 at 09:37:42PM +0100, Peter Zijlstra wrote: > > On Thu, 2008-01-31 at 23:39 +0530, Balbir Singh wrote: > > Srivatsa Vaddagiri wrote: > > > Hi, > > > As we were implementing multiple-hierarchy support for CPU > > > controller, we hit some oddities in its implementation, partly related > > > to current cgroups implementation. Peter and I have been debating on the > > > exact solution and I thought of bringing that discussion to lkml. > > > > > > Consider the cgroup filesystem structure for managing cpu resource. > > > > > > # mount -t cgroup -ocpu,cpuacct none /cgroup > > > # mkdir /cgroup/A > > > # mkdir /cgroup/B > > > # mkdir /cgroup/A/a1 > > > > > > will result in: > > > > > > /cgroup > > > |------<tasks> > > > |------<cpuacct.usage> > > > |------<cpu.shares> > > > | > > > |----[A] > > > | |----<tasks> > > > | |----<cpuacct.usage> > > > | |----<cpu.shares> > > > | | > > > | |---[a1] > > > | |----<tasks> > > > | |----<cpuacct.usage> > > > | |----<cpu.shares> > > > | | > > > | > > > |----[B] > > > | |----<tasks> > > > | |----<cpuacct.usage> > > > | |----<cpu.shares> > > > | > > > > > > > > > Here are some questions that arise in this picture: > > > > > > 1. What is the relationship of the task-group in A/tasks with the > > > task-group in A/a1/tasks? In otherwords do they form siblings > > > of the same parent A? > > > > > > > I consider them to be the same relationship between directories and files. > > A/tasks are siblings of A/a1 and A/other children, *but* the entities of > > interest are A and A/a1. > > > > > 2. Somewhat related to the above question, how much resource should the > > > task-group A/a1/tasks get in relation to A/tasks? Is it 1/2 of parent > > > A's share or 1/(1 + N) of parent A's share (where N = number of tasks > > > in A/tasks)? > > > > > > > I propose that it gets 1/2 of the bandwidth, here is why > > > > 1. Assume that a task in A/tasks forks 1000 children, what happens to the > > bandwidth of A/a1's tasks then? We have no control over how many tasks can be > > created on A/tasks as a consequence of moving one task to A/tasks. Doing it the > > other way would mean, that A/a1/tasks will get 1/1001 of the bandwidth (sounds > > very unfair and prone to Denial of Service/Fairness) > > And I oppose this, it means not all siblings are treated equal. Also, I > miss the story of the 'hidden' group here. The biggest objection is this > hidden group with no direct controls. > > My proposal is to make it a hard constraint, either a group has task > children or a group has group children, but not mixed. That keeps the > interface explicit and doesn't hide the tricks we play. > That is one solution. Otherwise you provide the controls for the hidden group. (Namely the shares and the rt_ratio). I've been experimenting with this approach recently. <snip> > > > Note that user cannot create subdirectories under def_child with this > > > scheme! I am also not sure what impact this will have on other resources > > > like cpusets .. > > > I'm not sure why it would affect other resources? The def_child is not exposed to the cgroup filesystem. Could someone please explain it to me? > > > > Which means we'll need special logic in the cgroup filesystem to handle > > def_child. Not a very good idea. > > agreed. -- regards, Dhaval _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
