On Mon, Nov 15, 2021 at 04:10:29PM -0500, Waiman Long <longman@xxxxxxxxxx> wrote: > > On Mon, Oct 18, 2021 at 10:36:18AM -0400, Waiman Long <longman@xxxxxxxxxx> wrote: > > > + scheduler. Tasks in such a partition must be explicitly bound > > > + to each individual CPU. > [...] > > It can be a problem when one is trying to move from one cgroup to another > cgroup with non-overlapping cpus laterally. However, if a task is initially > from a parent cgroup with affinity mask that include cpus in the isolated > child cgroup, I believe it should be able to move to the isolated child > cgroup without problem. Otherwise, it is a bug that needs to be fixed. app_root cpuset.cpus=0-3 `- non_rt cpuset.cpus=0-1 cpuset.cpus.partition=member `- rt cpuset.cpus=2-3 cpuset.cpus.partition=isolated The app_root would have cpuset.cpus.effective=0-1 so even the task in app_root can't sched_setaffinity() to cpus 2-3. But AFAICS, the migration calls set_cpus_allowed_ptr() anyway, so the task in the isolated partition needn't to bind explicitly with sched_setaffinity(). (It'd have two cpus available, so one more sched_setaffinity() or migration into a single-cpu list is desirable.) All in all, I think the behavior is OK and the explicit binding of tasks in an isolated cpuset is optional (not a must as worded currently). > I think the wording may be confusing. What I meant is none of the requested > cpu can be granted. So if there is at least one granted, the effective cpus > won't be empty. Ack. > You currently cannot make change to cpuset.cpus that violates the cpu > exclusivity rule. The above constraints will not disallow you to make the > change. They just affect the validity of the partition root. Sibling exclusivity should be a validity condition regardless of whether transition is allowed or not. (At least it looks simpler to me.) > > > + Changing a partition root to "member" is always allowed. > > > + If there are child partition roots underneath it, however, > > > + they will be forced to be switched back to "member" too and > > > + lose their partitions. So care must be taken to double check > > > + for this condition before disabling a partition root. > > (Or is this how delegation is intended?) However, AFAICS, parent still > > can't remove cpuset.cpus even when the child is a "member". Otherwise, > > I agree with the back-switch. > There are only 2 possibilities here. Either we force the child partitions to > be become members or invalid partition root. My point here was mostly about preempting the cpus (as a v2 specific feature). (I'm rather indifferent whether children turn into invalid roots or members.) Thanks, Michal
