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X is justifiably slow (2022)
I regularly hear or read statements like this: “X is slow but this is to be expected because it needs to do a lot of work”. It can be said about an application or a component in a larger system, and can refer to other resources that aren’t time. I often find these profoundly unhelpful as they depend much more on the speaker’s intuition and understanding of the problem, than X itself.
It’s common to see 10x gaps or more between different implementations of the same idea, and without profiling the code it’s hard to know whether something unexpected is taking the majority of time. The performance deficit between a reasonable serial implementation and code that uses efficient SIMD and multithreading can be significant - it’s not particularly outlandish to see 100x delta on modern multi core chips with wide SIMD on computationally intensive problems - and replacing drastically cache inefficient algorithms with cache efficient ones can also yield dramatic speedups. It can be very difficult to tell the difference, which is why I get annoyed a little bit every time I hear this, because the odds that enough analysis has been done on the particular implementation of the particular solution on the specific hardware and the exact data that’s being processed before the statement is made are slim.
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