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Go Optimization Guide

(goperf.dev)
480 points jedeusus | 1 comments | 31 Mar 25 20:29 UTC | HN request time: 0s | source
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nopurpose ◴[31 Mar 25 22:34 UTC] No.43540684[source]▶
Every perf guide recommends to minimize allocations to reduce GC times, but if you look at pprof of a Go app, GC mark phase is what takes time, not GC sweep. GC mark always starts with known live roots (goroutine stacks, globals, etc) and traverse references from there colouring every pointer. To minimize GC time it is best to avoid _long living_ allocations. Short lived allocations, those which GC mark phase will never reach, has almost neglible effect on GC times.

Allocations of any kind have an effect on triggering GC earlier, but in real apps it is almost hopeless to avoid GC, except for very carefully written programs with no dependenciesm, and if GC happens, then reducing GC mark times gives bigger bang for the buck.

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1. ncruces ◴[01 Apr 25 10:06 UTC] No.43544950[source]▶
The point is not to avoid GC entirely, but to reduce allocation pressure.

If you can avoid allocs in a hot loop, it definitely pays to do so. If you can't for some reason, and can use sync.Pool there, measure it.

Cutting allocs in half may not matter much, but if you can cut them by 99% because you were allocating in every iteration of a 1 million loop, and now aren't, it will make a difference, even if all those allocs die instantly.

I've gotten better than two fold performance increases on real code with both techniques.