Evaluate Profile-Guided Optimization (PGO) and LLVM BOLT

[zamazan4ik]

Hi!

Recently I checked Profile-Guided Optimization (PGO) improvements on multiple projects. The results are here. Since PGO shows improvements for many workloads, I think trying to optimize rumqttd with PGO can be a good idea.

I can suggest the following action points:

• Perform PGO benchmarks on rumqttd. And if it shows improvements - add a note about possible improvements in rumqttd's performance with PGO.
• Providing an easier way (e.g. a build option) to build scripts with PGO can be useful for the end-users and maintainers since they will be able to optimize rumqttd according to their own workloads.
• Optimize pre-built rumqttd binaries with PGO.

Here you can find examples of how PGO (and sometimes LLVM BOLT) is already integrated into different projects. Here are documentation examples with PGO in different projects.

Maybe testing Post-Link Optimization techniques (like LLVM BOLT) would be interesting too but I recommend starting from the usual PGO.

For the Rust projects, I suggest PGO optimizing with cargo-pgo (it supports LLVM BOLT too).