This paper studies the memory behavior of important Java workloads
used in benchmarking Java Virtual Machines (JVMs), based on
instrumentation of both application and library code in a
state-of-the-art JVM, and provides structured information about these
workloads to help guide systems' design. We begin by characterizing
the inherent memory behavior of the benchmarks, such as information on
the breakup of heap accesses among different categories and on the
hotness of references to fields and methods. We then provide detailed
information about misses in the data TLB and caches, including the
distribution of misses over different kinds of accesses and over
different methods. In the process, we make interesting discoveries
about TLB behavior and limitations of data prefetching schemes
discussed in the literature in dealing with pointer-intensive Java
codes. Throughout this paper, we develop a set of recommendations to
computer architects and compiler writers on how to optimize computer
systems and system software to run Java programs more efficiently.
This paper also makes the first attempt to compare the characteristics
of SPECjvm98 to those of a server-oriented benchmark, pBOB, and
explain why the current set of SPECjvm98 benchmarks may not be
adequate for a comprehensive and objective evaluation of JVMs and
just-in-time (JIT) compilers.
We discover that the fraction of accesses to array elements is quite
significant and demonstrate that the number of ``hot spots'' in the
benchmarks is small. We also show that even a fairly large L2 data
cache is not effective for many Java benchmarks. We observe that
instructions used to prefetch data into the L2 data cache are often
squashed because of high TLB miss rates and because the TLB does not
usually have the translation information needed to prefetch the data
into the L2 data cache. We also find that co-allocation of frequently
used method tables can reduce the number of TLB misses and lower the
cost of accessing type information block entries in virtual method
calls and runtime type checking.
By: Yefim Shuf , Mauricio J. Serrano , Manish Gupta , Jaswinder Pal Sin
Published in: RC22296 in 2002
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