diff options
Diffstat (limited to 'Documentation/scheduler')
| -rw-r--r-- | Documentation/scheduler/sched-deadline.txt | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt index 73ef489fcecf..c794ebfc08a5 100644 --- a/Documentation/scheduler/sched-deadline.txt +++ b/Documentation/scheduler/sched-deadline.txt @@ -133,7 +133,7 @@ CONTENTS arrival time r_j (the time when the job starts), an amount of computation time c_j needed to finish the job, and a job absolute deadline d_j, which is the time within which the job should be finished. The maximum execution - time max_j{c_j} is called "Worst Case Execution Time" (WCET) for the task. + time max{c_j} is called "Worst Case Execution Time" (WCET) for the task. A real-time task can be periodic with period P if r_{j+1} = r_j + P, or sporadic with minimum inter-arrival time P is r_{j+1} >= r_j + P. Finally, d_j = r_j + D, where D is the task's relative deadline. @@ -141,7 +141,7 @@ CONTENTS WCET and its period (or minimum inter-arrival time), and represents the fraction of CPU time needed to execute the task. - If the total utilization sum_i(WCET_i/P_i) is larger than M (with M equal + If the total utilization U=sum(WCET_i/P_i) is larger than M (with M equal to the number of CPUs), then the scheduler is unable to respect all the deadlines. Note that total utilization is defined as the sum of the utilizations @@ -159,8 +159,8 @@ CONTENTS More precisely, it can be proven that using a global EDF scheduler the maximum tardiness of each task is smaller or equal than ((M − 1) · WCET_max − WCET_min)/(M − (M − 2) · U_max) + WCET_max - where WCET_max = max_i{WCET_i} is the maximum WCET, WCET_min=min_i{WCET_i} - is the minimum WCET, and U_max = max_i{WCET_i/P_i} is the maximum utilization. + where WCET_max = max{WCET_i} is the maximum WCET, WCET_min=min{WCET_i} + is the minimum WCET, and U_max = max{WCET_i/P_i} is the maximum utilization. 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 @@ -170,7 +170,7 @@ CONTENTS of the tasks running on such a CPU is smaller or equal than 1. If D_i != P_i for some task, then it is possible to define the density of a task as WCET_i/min{D_i,P_i}, and EDF is able to respect all the deadlines - of all the tasks running on a CPU if the sum sum_i WCET_i/min{D_i,P_i} of the + of all the tasks running on a CPU if the sum sum(WCET_i/min{D_i,P_i}) of the densities of the tasks running on such a CPU is smaller or equal than 1 (notice that this condition is only sufficient, and not necessary). |