7,576 research outputs found
A PROCESSOR UTILIZATION MODEL FOR A MULTIPROCESSOR COMPUTER SYSTEM
A processor utilization model for a simplified multiprocessor computer
system is developed. Jobs are assumed to arrive according to a general input
process, and each job is assigned randomly to an available processor. A
finite capacity input buffer is used if no processor is available. The mathematical model is based on the busy period analysis, and two utilization
measures are derived:
(1) processor utilization when the system is busy (the fraction of processor occupation time during a busy period), and
(2) global processor utilization (the fraction of processor occupation time during a busy cycle).
Additionally, the arbitrary time state probability distribution is obtained
and serves as the basis for the above measures in addition to others. Several
approximations enable the development of a computational model from the mathematical model. Experimentation with the computational model reveals the sensitivity
of the model to variability in the arrival process. Comparison of 2-processor
and 4-processor systems from the operator perspective indicates a qualified
preference for the behavior of the 2-processor system. This preference must
be carefully interpreted since processor costs, the increase in overhead with an
increase in processors, and behavioral variables reflecting the user perspective
are excluded
Problems related to the integration of fault tolerant aircraft electronic systems
Problems related to the design of the hardware for an integrated aircraft electronic system are considered. Taxonomies of concurrent systems are reviewed and a new taxonomy is proposed. An informal methodology intended to identify feasible regions of the taxonomic design space is described. Specific tools are recommended for use in the methodology. Based on the methodology, a preliminary strawman integrated fault tolerant aircraft electronic system is proposed. Next, problems related to the programming and control of inegrated aircraft electronic systems are discussed. Issues of system resource management, including the scheduling and allocation of real time periodic tasks in a multiprocessor environment, are treated in detail. The role of software design in integrated fault tolerant aircraft electronic systems is discussed. Conclusions and recommendations for further work are included
Integrating Job Parallelism in Real-Time Scheduling Theory
We investigate the global scheduling of sporadic, implicit deadline,
real-time task systems on multiprocessor platforms. We provide a task model
which integrates job parallelism. We prove that the time-complexity of the
feasibility problem of these systems is linear relatively to the number of
(sporadic) tasks for a fixed number of processors. We propose a scheduling
algorithm theoretically optimal (i.e., preemptions and migrations neglected).
Moreover, we provide an exact feasibility utilization bound. Lastly, we propose
a technique to limit the number of migrations and preemptions
Packing Sporadic Real-Time Tasks on Identical Multiprocessor Systems
In real-time systems, in addition to the functional correctness recurrent
tasks must fulfill timing constraints to ensure the correct behavior of the
system. Partitioned scheduling is widely used in real-time systems, i.e., the
tasks are statically assigned onto processors while ensuring that all timing
constraints are met. The decision version of the problem, which is to check
whether the deadline constraints of tasks can be satisfied on a given number of
identical processors, has been known -complete in the strong sense.
Several studies on this problem are based on approximations involving resource
augmentation, i.e., speeding up individual processors. This paper studies
another type of resource augmentation by allocating additional processors, a
topic that has not been explored until recently. We provide polynomial-time
algorithms and analysis, in which the approximation factors are dependent upon
the input instances. Specifically, the factors are related to the maximum ratio
of the period to the relative deadline of a task in the given task set. We also
show that these algorithms unfortunately cannot achieve a constant
approximation factor for general cases. Furthermore, we prove that the problem
does not admit any asymptotic polynomial-time approximation scheme (APTAS)
unless when the task set has constrained deadlines, i.e.,
the relative deadline of a task is no more than the period of the task.Comment: Accepted and to appear in ISAAC 2018, Yi-Lan, Taiwa
- …