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Comment by rubber_duck | Hacker News Reader

Great article, this isn't my domain so the results are unexpected and the fact that a domain expert working on the problem can miss stuff like this reinforces something I see over and over when it comes to optimization - forget your assumption, intuition and best practices - everything is context sensitive (size of data, hardware specific) and gets obsolete through hardware evolution - the only way to optimise is to measure to identify bottlenecks after you have working code and them test again that you actually succeeded - don't optimise in advance.

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And measure. Always measure. Without data it’s all posturing

the opposition usually sounds like this - "Microbenchmarks lie". On one of the past projects, the leading engineers and architects just loved that phrase and voiced it like a deep profound truth understanding of which was a hallmark of belonging to their circle of chosen. Any specific measurements showing issues with the supposedly brilliant architecture and implementation choices of that project (with many of these choices following the latest "best practices" fads published by some venerable technologists) were dismissed by that phrase just like by magic. Naturally that was one of the slowest, not to mention buggy, projects in my experience, and working in the enterprise space i've seen my share of slow and buggy.

Microbenchmarks are not lying, but they can be misleading...

The most frequent problem is selecting the fastest solution with a microbenchmark and creating a lot of unnecessary cache eviction/pollution, sometimes on the code cache, sometimes on L1/L2 or both...

Microbenchmarks are good to explore the optimization space, but the final decision should be made with the full execution context in mind.

Except that's not opposition? Microbenchmarks do, always, lie; you need to measure the performance of your actual, real code that you're actually caring about the speed of.

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