SRC Technical Note 1997-016
Continuous Profiling: Where Have All the Cycles Gone?
Jennifer M. Anderson, Lance M. Berc, Jeffrey Dean, Sanjay Ghemawat, Monika
R. Henzinger, Shun-Tak A. Leung, Richard L. Sites, Mark T. Vandevoorde, Carle A.
Waldspurger, William E. Weihl
Note #1997-016. July 28, 1997
This paper describes the DIGITAL Continuous Profiling Infrastructure, a
sampling-based profiling system designed to run continuously on production
systems. The system supports multiprocessors, works on unmodified executables,
and collects profiles for entire systems, including user programs, shared
libraries, and the operating system kernel. Samples are collected at a high rate
(over 5200 samples/sec per 333-MHz processor), yet with low overhead (1-3%
slowdown for most workloads).
Analysis tools supplied with the profiling system use the sample data to
produce an accurate accounting, down to the level of pipeline stalls incurred by
individual instructions, of where time is being spent. When instructions incur
stalls, the tools identify possible reasons, such as cache misses, branch
mispredictions, and functional unit contention. The fine-grained
instruction-level analysis guides users and automated optimizers to the causes
of performance problems and provides important insights for fixing them.
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