On The Complexity Of Scheduling With Communication Delay And Contention

We show the NP-Completeness of two processor scheduling with tasks of execution time 1 or 2 units and unit interprocessor communication latency. We develop a model of scheduling in the presence of communication contention, and show the NP-Completeness of two processor scheduling with unit execution time tasks in our model. Keywords: Precedence Constrained Scheduling, Interprocessor Communication Delays, Message Contention, NP Completeness 1. Introduction We consider scheduling models in which the computation is modelled as a set of tasks which are executed independently, sequentially and non-preemptively at times which are consistent with a partial order specified as an acyclic directed graph (dag). We are interested in the case where the tasks are executed on identical processors according to the definition used by, for example, Graham et al. [1]. In scheduling models the edges in the dag imply precedence and also, in some sense data flow. If tasks connected by an edge are uniquely..

Much Ado About Shared-Nothing

In a `shared-nothing' parallel computer, each processor has its own memory and disks and processors communicate by passing messages through an interconnect. Many academic researchers, and some vendors, assert that shared-nothingness is the `consensus' architecture for parallel DBMSs. This alleged consensus is used as a justification for simulation models, algorithms, research prototypes and even marketing campaigns. We argue that shared-nothingness is no longer the consensus hardware architecture and that hardware resource sharing is a poor basis for categorising parallel DBMS software architectures if one wishes to compare the performance characteristics of parallel DBMS products. 1 Introduction A parallel computer has a `shared-nothing' architecture if each processor has its own memory and its own disk sub-system; pro- Tel. + 44 131 553 3313, Fax + 44 131 555 1178, Email: [email protected] y King's Buildings, JCMB, Edinburgh EH9 3JZ, Scotland, Tel. + 44 131 6505133, Fax ..

Models of Machines and Computation for Mapping in Multicomputers

It is now more than a quarter of a century since researchers started publishing papers on mapping strategies for distributing computation across the computation resources of multiprocessor systems. There exists a large body of literature on the subject, but there is no commonly-accepted framework whereby results in the field can be compared. Nor is it always easy to assess the relevance of a new result to a particular problem. Furthermore, changes in parallel computing technology have made some of the earlier work of less relevance to current multiprocessor systems. In this paper versions of the mapping problem are classified, and research in the field is considered in terms of its relevance to the problem of programming currently available hardware in the form of a distributed memory multiple instruction stream multiple data stream computer: a multicomputer . Categories and Subject Descriptors: C.1.2 [Multiple Data Stream Architectures ]:Multiprocessors, Parallel Processors; C.2.1 [..

Nucleic Acid-Sensing Toll-like Receptors Are Essential for the Control of Endogenous Retrovirus Viremia and ERV-Induced Tumors

SummaryThe genome of vertebrates contains endogenous retroviruses (ERVs) that are largely nonfunctional relicts of ancestral germline infection by exogenous retroviruses. However, in some mouse strains ERVs are actively involved in disease. Here we report that nucleic acid-recognizing Toll-like receptors 3, 7, and 9 (TLR 3, TLR7, and TLR9) are essential for the control of ERVs. Loss of TLR7 function caused spontaneous retroviral viremia that coincided with the absence of ERV-specific antibodies. Importantly, additional TLR3 and TLR9 deficiency led to acute T cell lymphoblastic leukemia, underscoring a prominent role for TLR3 and TLR9 in surveillance of ERV-induced tumors. Experimental ERV infection induced a TLR3-, TLR7-, and TLR9-dependent group of “acute-phase” genes previously described in HIV and SIV infections. Our study suggests that in addition to their role in innate immunity against exogenous pathogens, nucleic acid-recognizing TLRs contribute to the immune control of activated ERVs and ERV-induced tumors