Slowing down programs is surprisingly useful

Summary

Most research on programming language performance asks a variation of a single question: how can we make some specific program faster? Sometimes we may even investigate how we can use less memory. This means a lot of research focuses solely on reducing the amount of resources needed to achieve some computational goal. So, why on earth might we be interested in slowing down programs then? Slowing Down Programs is Surprisingly Useful! Making programs slower can be useful to find race conditions, to simulate speedups, and to assess how accurate profilers are. To detect race conditions, we may want to use an approach similar to fuzzing. Instead of exploring a program’s implementation by varying its input, we can explore different instruction interleavings, thread or event schedules, by slowing down program parts to change timings. This approach allows us to identify concurrency bugs and is used by CHESS, WAFFLE, and NACD. The Coz profiler is an example of how slowing down programs can be used to simulate speedup. With Coz, we can estimate whether an optimization is beneficial before implementing it. Coz simulates it by slowing down all other program parts. The part we think might be optimizable stays at the same speed it was before, but is now virtually sped up, which allows us to see whether it gives enough of a benefit to justify a perhaps lengthy optimization project. And, as mentioned before, we can also use it to assess how accurate profilers are. Though, I’ll leave this for the next blog posts. :) The current approaches to slowing down programs for these use cases are rather coarse-grained though. Race detection often adapts the scheduler or uses, for example, APIs such as Thread.sleep(). Similarly, Coz pauses the execution of the other threads. Work on measuring whether profilers give actionable results, inserts bytecodes into Java programs to compute Fibonacci numbers. By using more fine-grained slowdowns, we think we could make race detection, speedup estimatio...