Processor allocation and job scheduling are com¬ plementary techniques to improve the performance of multiprocessors. It has been observed that all the hypercube allocation policies with the FCFS schedul¬ ing show little performance difference. A greater im¬ pact on the performance can be obtained by efficient job scheduling. This paper presents an effort in that direction by introducing a new scheduling algorithm called lazy scheduling for hypercubes. The motivation of this scheme is to eliminate the limitations of the FCFS scheduling. This is done by maintaining sep¬ arate queues for different job sizes and delaying the allocation of a job if any other job(s) of the same di¬ mension is(are) running in the system. Simulation studies show that the hypercube performance is dra¬ matically enhanced by using the lazy scheme as com¬ pared to the FCFS scheduling. Comparison with a re¬ cently proposed scheme called scan indicates that the lazy scheme performs better than scan under a wide range of workloads.

No abstract

No abstract

Many optimization schemes have been proposed to reduce the overhead of checkpointing. Incremental checkpointing based on memory page protection has been one of the successful schemes used to reduce the overhead and to improve the performance of checkpointing. In this paper, we propose two checkpointing schemes, called "block encoding'' and "combined block encoding", which further reduce the checkpointing overhead. The smallest unit of checkpoint data in OUT scheme is a block, which is smaller than a pagethis reduces the amount of checkpoint data required when compared with page-based incremental checkpointing.One drawback of the proposed schemes is the possibility of aliasing in encoded words. In this paper, however, we show that the aliasing probability is near zero when an &byte encoded word is used. The performance of the proposed schemes as analyzed and measured using experiments. First. we construct a n analytic model that predicts the checkpointing overhead. B y using this model, we can estimate the block size that produces the best performance for a given target program. Next, the proposed schemes are implemented on libckpt , a general-purpose checkpointing library for Unix based system which was developed at the University of Tennessee. According to OUT experimental results, the proposed schemes reduce the overhead by 11.7% in the best case and increase the overhead by 0.5% in the worst case in comparison with page-based incremental checkpointing. In most cases, the combined block encoding scheme shows an improvement over both block encoding and page-based incremental checkpointing.

No abstract