Messages in this thread | | | Date | Sat, 19 May 2012 13:37:36 -0700 | Subject | Re: [PATCH] sched/rt: fix SCHED_RR across cgroups | From | Colin Cross <> |
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On Sat, May 19, 2012 at 6:11 AM, Dario Faggioli <raistlin@linux.it> wrote: > On Fri, 2012-05-18 at 17:13 -0700, Colin Cross wrote: >> Even with this patch, scheduling of SCHED_RR tasks in cgroups is a >> little odd. Each cgroup is treated as a schedulable entity alongside >> the tasks in the same parent cgroup, and then the tasks inside the >> child cgroup round robin through the child cgroup's time slices. So >> in the setup: >> root_cgroup >> task 1 >> cgroup >> task 2 >> task 3 >> >> The RR will be: >> task 1, cgroup(task 2), task 1, cgroup(task 3), ... >> >> task 1 will run twice as often, for a full RR_TIMESLICE each time, as >> tasks 2 and 3. >> > That looks right to me... > >> Is that the way SCHED_RR is intended to interact with cgroups? >> > I would say it is. That's what you get because of putting task1 and > cgroup at the same level in the "hierarchy". I'm curious, what kind of > behaviour were you expecting?
That behavior matches exactly with scheduling of normal tasks and cgroups with default cpu.shares, but doesn't match too well with what I can see of the posix SCHED_RR description, which suggests all the SCHED_RR threads go into a single queue. I was just curious if the behavior my patch restored was correct, since it can't be adjusted by tweaking any parameters like cpu.shares.
> Of course, the actual schedule also depends on the real-time priority of > the various tasks (groups don't have a priority, they inherit it from > their tasks, or at least it was like this when I used to work with > it :-P), but I guess you're putting all the tasks in the same queue > (i.e., same rt-prio), is it that the case?
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