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| -rw-r--r-- | Documentation/scheduler/sched-deadline.txt | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt index 2a924e19912a..e114513a2731 100644 --- a/Documentation/scheduler/sched-deadline.txt +++ b/Documentation/scheduler/sched-deadline.txt @@ -8,6 +8,10 @@ CONTENTS 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 @@ CONTENTS 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 @@ CONTENTS 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 @@ CONTENTS 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 @@ CONTENTS 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) |