4,597 research outputs found
SELFISHMIGRATE: A Scalable Algorithm for Non-clairvoyantly Scheduling Heterogeneous Processors
We consider the classical problem of minimizing the total weighted flow-time
for unrelated machines in the online \emph{non-clairvoyant} setting. In this
problem, a set of jobs arrive over time to be scheduled on a set of
machines. Each job has processing length , weight , and is
processed at a rate of when scheduled on machine . The online
scheduler knows the values of and upon arrival of the job,
but is not aware of the quantity . We present the {\em first} online
algorithm that is {\em scalable} ((1+\eps)-speed
-competitive for any constant \eps > 0) for the
total weighted flow-time objective. No non-trivial results were known for this
setting, except for the most basic case of identical machines. Our result
resolves a major open problem in online scheduling theory. Moreover, we also
show that no job needs more than a logarithmic number of migrations. We further
extend our result and give a scalable algorithm for the objective of minimizing
total weighted flow-time plus energy cost for the case of unrelated machines
and obtain a scalable algorithm. The key algorithmic idea is to let jobs
migrate selfishly until they converge to an equilibrium. Towards this end, we
define a game where each job's utility which is closely tied to the
instantaneous increase in the objective the job is responsible for, and each
machine declares a policy that assigns priorities to jobs based on when they
migrate to it, and the execution speeds. This has a spirit similar to
coordination mechanisms that attempt to achieve near optimum welfare in the
presence of selfish agents (jobs). To the best our knowledge, this is the first
work that demonstrates the usefulness of ideas from coordination mechanisms and
Nash equilibria for designing and analyzing online algorithms
A Concurrency Control Method Based on Commitment Ordering in Mobile Databases
Disconnection of mobile clients from server, in an unclear time and for an
unknown duration, due to mobility of mobile clients, is the most important
challenges for concurrency control in mobile database with client-server model.
Applying pessimistic common classic methods of concurrency control (like 2pl)
in mobile database leads to long duration blocking and increasing waiting time
of transactions. Because of high rate of aborting transactions, optimistic
methods aren`t appropriate in mobile database. In this article, OPCOT
concurrency control algorithm is introduced based on optimistic concurrency
control method. Reducing communications between mobile client and server,
decreasing blocking rate and deadlock of transactions, and increasing
concurrency degree are the most important motivation of using optimistic method
as the basis method of OPCOT algorithm. To reduce abortion rate of
transactions, in execution time of transactions` operators a timestamp is
assigned to them. In other to checking commitment ordering property of
scheduler, the assigned timestamp is used in server on time of commitment. In
this article, serializability of OPCOT algorithm scheduler has been proved by
using serializability graph. Results of evaluating simulation show that OPCOT
algorithm decreases abortion rate and waiting time of transactions in compare
to 2pl and optimistic algorithms.Comment: 15 pages, 13 figures, Journal: International Journal of Database
Management Systems (IJDMS
Impact of inter-cell interference on flow level performance of scheduling schemes for the UMTS EUL
The UMTS Enhanced Uplink (EUL) is expected to provide higher capacity, increased data rates, and smaller latency on the communication link from users towards the network. A key mechanism in EUL traffic handling is the packet scheduler, for which a number of basic schemes can be identified (one-by- one, partial parallel, and full parallel). In this paper we analyze the interaction between the EUL scheduling scheme deployed in the network and the inter-cell interference. On the one hand, different scheduling schemes cause different inter-cell interference patterns on neighbouring cells. On the other hand, the different schemes are affected by inter-cell interference in different ways. The scheduling schemes are evaluated and compared under different approaches for reserving part of the allowed noise rise at the base station for inter-cell interference. For our analysis, we have developed a hybrid analytical/simulation approach allowing for fast evaluation of performance measures such as the mean flow transfer time and fairness expressing how the performance depends on the user’s location. This approach takes into account both the packet-level characteristics and the flow-level dynamics due to the random user behaviour
Efficient Parallelization of Short-Range Molecular Dynamics Simulations on Many-Core Systems
This article introduces a highly parallel algorithm for molecular dynamics
simulations with short-range forces on single node multi- and many-core
systems. The algorithm is designed to achieve high parallel speedups for
strongly inhomogeneous systems like nanodevices or nanostructured materials. In
the proposed scheme the calculation of the forces and the generation of
neighbor lists is divided into small tasks. The tasks are then executed by a
thread pool according to a dependent task schedule. This schedule is
constructed in such a way that a particle is never accessed by two threads at
the same time.Benchmark simulations on a typical 12 core machine show that the
described algorithm achieves excellent parallel efficiencies above 80 % for
different kinds of systems and all numbers of cores. For inhomogeneous systems
the speedups are strongly superior to those obtained with spatial
decomposition. Further benchmarks were performed on an Intel Xeon Phi
coprocessor. These simulations demonstrate that the algorithm scales well to
large numbers of cores.Comment: 12 pages, 8 figure
- …