sched/dl/Documentation: Split Section 3
Introduce 4 subsections to make Section 3 more readable.
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/1431954032-16473-10-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt
index 2a924e1..e114513 100644
--- a/Documentation/scheduler/sched-deadline.txt
+++ b/Documentation/scheduler/sched-deadline.txt
@@ -8,6 +8,10 @@
1. Overview
2. Scheduling algorithm
3. Scheduling Real-Time Tasks
+ 3.1 Definitions
+ 3.2 Schedulability Analysis for Uniprocessor Systems
+ 3.3 Schedulability Analysis for Multiprocessor Systems
+ 3.4 Relationship with SCHED_DEADLINE Parameters
4. Bandwidth management
4.1 System-wide settings
4.2 Task interface
@@ -126,6 +130,9 @@
suited for periodic or sporadic real-time tasks that need guarantees on their
timing behavior, e.g., multimedia, streaming, control applications, etc.
+3.1 Definitions
+------------------------
+
A typical real-time task is composed of a repetition of computation phases
(task instances, or jobs) which are activated on a periodic or sporadic
fashion.
@@ -166,6 +173,9 @@
is the minimum WCET, and U_max = max{WCET_i/P_i} is the maximum
utilization[12].
+3.2 Schedulability Analysis for Uniprocessor Systems
+------------------------
+
If M=1 (uniprocessor system), or in case of partitioned scheduling (each
real-time task is statically assigned to one and only one CPU), it is
possible to formally check if all the deadlines are respected.
@@ -204,6 +214,9 @@
time-consuming to be performed on-line. Hence, as explained in Section
4 Linux uses an admission test based on the tasks' utilizations.
+3.3 Schedulability Analysis for Multiprocessor Systems
+------------------------
+
On multiprocessor systems with global EDF scheduling (non partitioned
systems), a sufficient test for schedulability can not be based on the
utilizations or densities: it can be shown that even if D_i = P_i task
@@ -249,6 +262,9 @@
the total utilization is smaller or equal than M then the response times of
the tasks are limited.
+3.4 Relationship with SCHED_DEADLINE Parameters
+------------------------
+
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)