Small functions need special attention not just because they show up as leaf nodes everywhere but also because they are difficult for profilers to account properly. You get two functions listed as each taking 4% of CPU time, and one could easily be taking up twice as much compute as the other. The sort of memory pressure that small functions can generate can end up scapegoating a big function that uses a large fraction of memory because it gets stuck with cold cache or lots of GC pressure from the piddly functions fouling the nest.
One of my best examples of this, I had a function reported as still taking 10% of cumulative run time, after I’d tweaked it as much as I could. But I’d set up a benchmark that called a code path a deterministic number of times and this function was getting called twice as much as it should. I found two sibling methods asking the same question and rearranged them so the answer came as an argument and nixed the duplicate call. I reran the benchmark and instead of getting a reduction of 5% (10/2), I got 20%. That was all memory pressure.
The worst memory pressure I ever fixed I saw a 10x improvement by removing one duplicate call. Now, there was a quadratic part of that call but it was a small enough n that I expected 3x and hoped for 4x, and was as shocked as anyone when it went from 30s to 3s with one refactor.
One of my best examples of this, I had a function reported as still taking 10% of cumulative run time, after I’d tweaked it as much as I could. But I’d set up a benchmark that called a code path a deterministic number of times and this function was getting called twice as much as it should. I found two sibling methods asking the same question and rearranged them so the answer came as an argument and nixed the duplicate call. I reran the benchmark and instead of getting a reduction of 5% (10/2), I got 20%. That was all memory pressure.
The worst memory pressure I ever fixed I saw a 10x improvement by removing one duplicate call. Now, there was a quadratic part of that call but it was a small enough n that I expected 3x and hoped for 4x, and was as shocked as anyone when it went from 30s to 3s with one refactor.