Re: [RFC][PATCH 02/22] sched: add extended scheduling interface

[Steven Rostedt]

On Fri, 2010-10-29 at 08:27 +0200, Raistlin wrote:

> +/*
> + * Extended scheduling parameters data structure.
> + *
> + * This is needed because the original struct sched_param can not be
> + * altered without introducing ABI issues with legacy applications
> + * (e.g., in sched_getparam()).
> + *
> + * However, the possibility of specifying more than just a priority for
> + * the tasks may be useful for a wide variety of application fields, e.g.,
> + * multimedia, streaming, automation and control, and many others.
> + *
> + * This variant (sched_param_ex) is meant at describing a so-called
> + * sporadic time-constrained task. In such model a task is specified by:
> + *  - the activation period or minimum instance inter-arrival time;
> + *  - the maximum (or average, depending on the actual scheduling
> + *    discipline) computation time of all instances, a.k.a. runtime;
> + *  - the deadline (relative to the actual activation time) of each
> + *    instance.
> + * Very briefly, a periodic (sporadic) task asks for the execution of
> + * some specific computation --which is typically called an instance--
> + * (at most) every period. Moreover, each instance typically lasts no more
> + * than the runtime and must be completed by time instant t equal to
> + * the instance activation time + the deadline.
> + *
> + * This is reflected by the actual fields of the sched_param_ex structure:
> + *
> + *  @sched_priority     task's priority (might still be useful)
> + *  @sched_deadline     representative of the task's deadline
> + *  @sched_runtime      representative of the task's runtime
> + *  @sched_period       representative of the task's period
> + *  @sched_flags        for customizing the scheduler behaviour
> + *
> + * There are other fields, which may be useful for implementing (in
> + * user-space) advanced scheduling behaviours, e.g., feedback scheduling:
> + *
> + *  @curr_runtime       task's currently available runtime
> + *  @used_runtime       task's totally used runtime
> + *  @curr_deadline      task's current absolute deadline
> + *
> + * Given this task model, there are a multiplicity of scheduling algorithms
> + * and policies, that can be used to ensure all the tasks will make their
> + * timing constraints.
> + */

A while ago I implemented an EDF scheduler for a client (before working
with Red Hat), and one thing they asked about was having a "soft group",
which was basically: This group is guaranteed X runtime in Y period, but
if the system is idle, let the group run, even if it has exhausted its X
runtime.

Is this supported?

-- Steve



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