15.12

Current generation CPUs include an instruction cache, which caches recently used instructions. A function call then has a significant overhead because the set of instructions being executed changes, resulting in cache misses on the instruction cache.

  1. Explain why producer-driven pipelining with buffering is likely to result in a better instruction cache hit rate, as compared to demand-driven pipelining.

  2. Explain why modifying demand-driven pipelining by generating multiple results on one call to next(), and returning them together, can improve the instruction cache hit rate.

  1. Explain why producer-driven pipelining with buffering is likely to result in a better instruction cache hit rate, as compared to demand-driven pipelining.

Producer-driven pipelining executes the same set of instructions to generate multiple tuples by consuming already generated tuples from the inputs. Thus instruction cache hits will be more. In comparison, demand-driven pipelining switches from the instructions of one function to another for each tuple, resulting in more misses.

  1. Explain why modifying demand-driven pipelining by generating multiple results on one call to next(), and returning them together, can improve the instruction cache hit rate.

By generating multiple results at one go, a next() function would receive multiple tuples in its inputs and have a loop that generates multiple tuples for its output without switching execution to another function. Thus, the instruction cache hit rate can be expected to improve.