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Comparison of Shared Virtual Memory across Uniprocessor and SMP Nodes

Report ID:
June 1997
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As the workstation market moves form single processor to small-scale
shared memory multiprocessors, it is very attractive to construct
larger-scale multiprocessors by connecting symmetric
multiprocessors (SMPs) with efficient commodity network interfaces
such as Myrinet Using a shared virtual memory (SVM) layer for
this purpose preserves the shared memory programming abstraction
across nodes. We explore the feasibility and performance implications
of one such approach by comparing the performance of two SVM protocols
on systems with uniprocessor and SMP nodes. AURC (Automatic Update
Release Consistency) is a protocol developed for the SHRIMP
multicomputer that takes advantage of the available Automatic Update
hardware support. HLRC (Home-Based Lazy Release Consistency) is an
all-software version of AURC. These protocols were demonstrated to
achieve good performance and to outperform earlier all-software
systems on configurations with uniprocessor nodes.

In this paper we use an architectural simulator and ten applications
to investigate the potential of using SMP nodes. Through detailed
simulations we find that using SMPs improves performance for most of
the applications, because of more sharing, effective prefetching and
lower synchronization costs. The protocols, however, exhibit different
behavior for some applications. HLRC is in general more robust and
predictable, whereas AURC exhibits more problems with contention
due to the increased traffic.

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