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SubjectRe: [PATCH 0/3] sched: use EDF to throttle RT task groups v2
On Tue, 2010-02-23 at 19:56 +0100, Fabio Checconi wrote:
> This patchset introduces a group level EDF scheduler extending the
> throttling mechanism, in order to make it support generic period
> assignments. With this patch, the runtime and period parameters
> can be used to specify arbitrary CPU reservations for RT tasks.
> From the previous post [1] I've integrated Peter's suggestions, using
> a multi-level hierarchy to do admission control, but a one-level only
> equivalent hierarchy for scheduling, and I've not removed the bandwidth
> migration mechanism, trying to adapt it to EDF scheduling. In this
> version tasks are still inserted into priority arrays and only groups
> are kept in a per-rq edf tree.
> The main design issues involved:
> - Since it is not easy to mix tasks and groups on the same scheduler
> queue (tasks have no deadlines), the bandwidth reserved to the tasks
> in a group is controlled with two additional cgroup attributes:
> rt_task_runtime_us and rt_task_period_us. These attributes control,
> within a cgroup, how much bandwidth is reserved to the tasks it
> contains. The old attributes, rt_runtime_us and rt_period_us, are
> still there, and control the bandwidth assigned to the cgroup. They
> are used only for admission control.
> - Shared resources are still handled using boosting. When a group
> contains a task inside a critical section it is scheduled according
> the highest priority among the ones of the tasks it contains.
> In this way, the same group has two modes: when it is not boosted
> it is scheduled according to its deadline; when it is boosted, it
> is scheduled according its priority. Boosted groups are always
> favored over non-boosted ones.
> - Given that the various rt_rq's belonging to the same task group
> are activated independently, there is the need of a timer per
> each rt_rq.
> - While balancing the bandwidth assigned to a cgroup on various cpus
> we have to make sure that utilization for the rt_rq's on each cpu
> does not exceed the global utilization limit for RT tasks.

> As usual, feedback welcome.

Looks very nice, good work! comments in individual replies.

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