Hi!

Recently I did many Profile-Guided Optimization (PGO) benchmarks on multiple projects - the results are available here. I think since the project is performance-oriented, it would be interesting to try to test PGO for optimizing tquic. I already did some benchmarks.

Test environment

• Fedora 38
• Linux kernel 6.5.5
• AMD Ryzen 9 5900x
• 48 Gib RAM
• SSD Samsung 980 Pro 2 Tib
• Compiler - Rustc 1.73
• tquic version: the latest for now from the develop branch on commit 05c56e7425ec1149a9c95ca7bbcb6acbab861fd6
• Disabled Turbo boost

Benchmark setup

For benchmarking purposes, I use the project's benchmarks. Release benchmarking is done with cargo bench, PGO optimized build is done with cargo-pgo with cargo pgo bench && cargo pgo optimize bench. PGO profiles are collected from the benchmark workload itself.

Results

I got the following results:

• Release + PGO-optimized compared to Release: https://gist.github.com/zamazan4ik/875e3d1948ac3db575bcbb442a6f6ebb
• (just for reference) PGO-Instrumented compared to Release: https://gist.github.com/zamazan4ik/f4af4f2e510d433253bf007ecb584507

According to the tests, PGO consistently improves tquic performance in some scenarios.

Further steps

I can suggest the following things to do:

• Evaluate PGO's applicability to tquic in more scenarios.
• If PGO helps to achieve better performance - add a note to tquic's documentation about that (probably somewhere in the README file). In this case, users and maintainers will be aware of another optimization opportunity for tquic.
• Maybe get some insights from the PGO profiles and optimize manually the code according to the profiles (maybe more aggressive inlining or something like that)