Garbage Collectors Affect Microbenchmarks

When comparing garbage collectors there are two key metrics: how much time is spent collecting garbage, and the maximum pause time. There’s another dimension to the choice of garbage collector though: how it instruments JIT compiled code and the consequences of that instrumentation. The cost of this instrumentation is usually a tiny price to pay […]

Observing Memory Level Parallelism with JMH

Quite some time ago I observed an effect where breaking a cache-inefficient shuffle algorithm into short stages could improve throughput: when cache misses were likely, an improvement could be seen in throughput as a function of stage length. The implementations benchmarked were as follows, where op is either precomputed (a closure over an array of […]

Limiting Factors in a Dot Product Calculation

The dot product is a simple calculation which reduces two vectors to the sum of their element-wise products. The calculation has a variety of applications and is used heavily in neural networks, linear regression and in search. What are the constraints on its computational performance? The combination of the computational simplicity and its streaming nature […]

Collecting Rocks and Benchmarks

As long as I can remember, I have been interested in rocks, I have hundreds of them in storage. Rocks are interesting because they hold little clues about processes nobody has ever seen happen. For instance, one of the first rocks I ever took an interest in was a smooth granite pebble, which I collected […]