sched/dl/Documentation: Switch to American English

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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/1431954032-16473-3-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 15:00:25 +02:00 committed by Ingo Molnar
parent 3aed357ee4
commit 3a3a58d406

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@ -43,7 +43,7 @@ CONTENTS
"deadline", to schedule tasks. A SCHED_DEADLINE task should receive
"runtime" microseconds of execution time every "period" microseconds, and
these "runtime" microseconds are available within "deadline" microseconds
from the beginning of the period. In order to implement this behaviour,
from the beginning of the period. In order to implement this behavior,
every time the task wakes up, the scheduler computes a "scheduling deadline"
consistent with the guarantee (using the CBS[2,3] algorithm). Tasks are then
scheduled using EDF[1] on these scheduling deadlines (the task with the
@ -63,7 +63,7 @@ CONTENTS
In more details, the CBS algorithm assigns scheduling deadlines to
tasks in the following way:
- Each SCHED_DEADLINE task is characterised by the "runtime",
- Each SCHED_DEADLINE task is characterized by the "runtime",
"deadline", and "period" parameters;
- The state of the task is described by a "scheduling deadline", and
@ -78,7 +78,7 @@ CONTENTS
then, if the scheduling deadline is smaller than the current time, or
this condition is verified, the scheduling deadline and the
remaining runtime are re-initialised as
remaining runtime are re-initialized as
scheduling deadline = current time + deadline
remaining runtime = runtime
@ -129,7 +129,7 @@ CONTENTS
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.
Each job J_j (where J_j is the j^th job of the task) is characterised by an
Each job J_j (where J_j is the j^th job of the task) is characterized by an
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
@ -137,20 +137,20 @@ CONTENTS
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.
The utilisation of a real-time task is defined as the ratio between its
The utilization of a real-time task is defined as the ratio between its
WCET and its period (or minimum inter-arrival time), and represents
the fraction of CPU time needed to execute the task.
If the total utilisation sum_i(WCET_i/P_i) is larger than M (with M equal
If the total utilization sum_i(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 utilisation is defined as the sum of the utilisations
Note that total utilization is defined as the sum of the utilizations
WCET_i/P_i over all the real-time tasks in the system. When considering
multiple real-time tasks, the parameters of the i-th task are indicated
with the "_i" suffix.
Moreover, if the total utilisation is larger than M, then we risk starving
Moreover, if the total utilization is larger than M, then we risk starving
non- real-time tasks by real-time tasks.
If, instead, the total utilisation is smaller than M, then non real-time
If, instead, the total utilization is smaller than M, then non real-time
tasks will not be starved and the system might be able to respect all the
deadlines.
As a matter of fact, in this case it is possible to provide an upper bound
@ -160,13 +160,13 @@ CONTENTS
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 utilisation.
is the minimum WCET, and U_max = max_i{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
possible to formally check if all the deadlines are respected.
If D_i = P_i for all tasks, then EDF is able to respect all the deadlines
of all the tasks executing on a CPU if and only if the total utilisation
of all the tasks executing on a CPU if and only if the total utilization
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 C_i/min{D_i,P_i}, and EDF is able to respect all the deadlines
@ -176,9 +176,9 @@ CONTENTS
On multiprocessor systems with global EDF scheduling (non partitioned
systems), a sufficient test for schedulability can not be based on the
utilisations (it can be shown that task sets with utilisations slightly
utilizations (it can be shown that task sets with utilizations slightly
larger than 1 can miss deadlines regardless of the number of CPUs M).
However, as previously stated, enforcing that the total utilisation is smaller
However, as previously stated, enforcing that the total utilization is smaller
than M is enough to guarantee that non real-time tasks are not starved and
that the tardiness of real-time tasks has an upper bound.
@ -218,10 +218,10 @@ CONTENTS
no guarantee can be given on the actual scheduling of the -deadline tasks.
As already stated in Section 3, a necessary condition to be respected to
correctly schedule a set of real-time tasks is that the total utilisation
correctly schedule a set of real-time tasks is that the total utilization
is smaller than M. When talking about -deadline tasks, this requires that
the sum of the ratio between runtime and period for all tasks is smaller
than M. Notice that the ratio runtime/period is equivalent to the utilisation
than M. Notice that the ratio runtime/period is equivalent to the utilization
of a "traditional" real-time task, and is also often referred to as
"bandwidth".
The interface used to control the CPU bandwidth that can be allocated
@ -251,7 +251,7 @@ CONTENTS
The system wide settings are configured under the /proc virtual file system.
For now the -rt knobs are used for -deadline admission control and the
-deadline runtime is accounted against the -rt runtime. We realise that this
-deadline runtime is accounted against the -rt runtime. We realize that this
isn't entirely desirable; however, it is better to have a small interface for
now, and be able to change it easily later. The ideal situation (see 5.) is to
run -rt tasks from a -deadline server; in which case the -rt bandwidth is a