For a typical program, I bet that the overall impact of the glibc allocator is well under 0.1%. If you can choose between < 0.1% and < 0.12%, I guess it matters in some sense, but not in any practical way. We almost never spend time on other sub-0.1% optimizations. You could probably squeeze a lot more by optimizing CPU branch predictor performance, minimizing CPU cache misses, or fine-tuning the scheduling strategy, but we also don't bother. 'Tis is the era of "native" apps written in Electron.