[WJW]

Woop! My timerfd change is finally out in the wild!

This will make it so that (on systems with timerfd) the runtime will no longer have to wait for the next runtime tick before exiting. This saves on average 5 ms per program run, and up to 10 ms for programs with a very short runtime. Not much for server programs with an expected lifetime of days/weeks, but potentially quite nice for CLI programs like hledger or for programs that invoke many other Haskell programs.

I accidentally discovered this when trying to optimize an Advent of Code problem and couldn't get it below 10 ms no matter what I tried. Eventually I discovered that "hello world" also took 10 ms so I assumed it was just runtime startup costs. Decided to look anyway and found out it was actually runtime shutdown costs, where the runtime would `join` the rts "ticker" thread. The ticker thread would only check for a shutdown flag once every loop, so 10 ms with the default settings. Now it can be shut down immediately, which makes small programs much faster.

[pja]

Oh wow. I’ll have to recompile some of my old AoC Code to see how fast it really runs now!

Like you I had assumed this was simply runtime startup / teardown overhead.