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sched/dl/Documentation: Clarify the relationship between tasks' deadlines and absolute scheduling deadlines

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Clarify what is the relationship between tasks' parameters and scheduling
parameters, explaining how to set the scheduling parameters so that all the
absolute deadlines of a task are respected.

Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: henrik@austad.us
Cc: juri.lelli@gmail.com
Cc: raistlin@linux.it
Link: http://lkml.kernel.org/r/1431954032-16473-9-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Luca Abeni 2015-05-18 15:00:31 +02:00 committed by Ingo Molnar
parent 134136c4b7
commit 7874085890
1 changed files with 11 additions and 3 deletions
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14
Documentation/scheduler/sched-deadline.txt
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@ -249,9 +249,17 @@ CONTENTS
the total utilization is smaller or equal than M then the response times of
the tasks are limited.
SCHED_DEADLINE can be used to schedule real-time tasks guaranteeing that
the jobs' deadlines of a task are respected. In order to do this, a task
must be scheduled by setting:
Finally, it is important to understand the relationship between the
SCHED_DEADLINE scheduling parameters described in Section 2 (runtime,
deadline and period) and the real-time task parameters (WCET, D, P)
described in this section. Note that the tasks' temporal constraints are
represented by its absolute deadlines d_j = r_j + D described above, while
SCHED_DEADLINE schedules the tasks according to scheduling deadlines (see
Section 2).
If an admission test is used to guarantee that the scheduling deadlines
are respected, then SCHED_DEADLINE can be used to schedule real-time tasks
guaranteeing that all the jobs' deadlines of a task are respected.
In order to do this, a task must be scheduled by setting:
- runtime >= WCET
- deadline = D