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by hinkley 189 days ago
Until you get high memory contention from the rest of the code. Once eviction gets high you get some pretty counterintuitive improvements by fixing things that seem like they shouldn’t need to be fixed.

My best documented case was a 10x speed up from removing a double lookup that was killing caches.
1 comments
crest 189 days ago
My best improvment was just bit-interleaving both axes of a 2x32bit integer coordinate (aka z-curve). I obtained factor ~100x (yes factor not percent) throughput improvement over locality in only one dimension. All it took was ~10 lines of bit twiddling. The runtime went from a bit above 300ms to slightly less then 3ms.
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hinkley 189 days ago
End to end gets weird. I was asked to look at an admin page, nobody could figure out why it was 30s. Literally the first thing I tried got it under 4 and the second down to three. It was pulling the same list of rows twice, applying two filters and then looking at the intersection. I changed the signature to send the list as input instead of the query constraints. Then I changed them to avoid the intersect.

If you would have asked me to bet on which one would have had the bigger impact I would have split the difference.

My second favorite was similar. Two functions making a call instead of sharing the answer. Profiler said 10% cumulative. I removed half. Instead of 5% I got 20%. Which just demonstrates how much data a profiler cannot show you.

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throw-the-towel 189 days ago
I'm wondering how do you folk even come up with this kind of optimisations.
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hinkley 189 days ago
Sheer stubbornness.

Profilers lie and some more than most. I’ve gotten 3x from code with a perfectly rectangular profile output.

Part of it comes down to a trick game devs steal from finance: give each task a budget and keep it to the budget even if it’s not the tall tent pole.

You should not spend 10% of your response time on telemetry and logging combined. Yet I pulled 10% TTFB out of just the logging and telemetry code on a project. It was a frog boiling situation. Every new epic used the new code and determining the cumulative cost wasn’t easy.

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