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docs(connlib): add profiling instructions (#6643)

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Documents profiling instructions that I've figured out over the last
couple of days. Since Rust 1.79, the standard library is compiled with
frame pointers enabled [0]. Grabbing stack-trace information from the
frame pointer makes profiling much easier because the data is just there
in-line. Using debug information (via `dwarf`) is also possible but
requires post-processing of the performance profile with `addr2line`
(`perf script` does that automatically). This can take multiple minutes
or longer, depending on the sampling frequency of the captured
performance data. This makes benchmarking almost infeasible because the
feedback loop is simply too long. Using frame pointers is a much nicer
experience.

The downside is that the application themselves also needs to be
compiled with frame pointers. We achieve that by setting the appropriate
compiler option in `.cargo/config.toml`. Ubuntu [1], Fedora [2] and Arch
[3] also ship all of their code with frame pointers enabled. Also, tech
giants such as Google & Meta have been running their systems with frame
pointers on-by-default for years [4].

[0]:
https://blog.rust-lang.org/2024/06/13/Rust-1.79.0.html#frame-pointers-enabled-in-standard-library-builds
[1]:
https://www.brendangregg.com/blog/2024-03-17/the-return-of-the-frame-pointers.html
[2]: https://pagure.io/fesco/issue/2923
[3]: https://gitlab.archlinux.org/archlinux/rfcs/-/merge_requests/26
[4]:
https://www.brendangregg.com/blog/2024-03-17/the-return-of-the-frame-pointers.html
This commit is contained in:
Thomas Eizinger
2024-09-10 10:00:00 -04:00
committed by GitHub
parent 2d51a91610
commit 5bf3230c62
3 changed files with 22 additions and 4 deletions
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5
rust/.cargo/config.toml Normal file
View File

@@ -0,0 +1,5 @@
[target.x86_64-unknown-linux-musl]
rustflags="-C force-frame-pointers=yes"
[target.x86_64-unknown-linux-gnu]
rustflags="-C force-frame-pointers=yes"

7
rust/Cargo.toml
View File

@@ -92,6 +92,9 @@ lto = "fat"
# at the expense of compilation time
codegen-units = 1
[profile.bench]
strip = false # Frame pointers are necessary for profiling; `strip=true` appears to remove them.
# Override build settings just for the GUI client, so we get a pdb/dwp
# Cargo ignores profile settings if they're not in the workspace's Cargo.toml
[profile.dev.package.firezone-gui-client]
@@ -103,7 +106,3 @@ strip = "none"
debug = "full"
split-debuginfo = "packed"
strip = "none"
# Override build settings for the relay, so we can capture flamegraphs
[profile.release.package.firezone-relay]
debug = "full"

14
rust/README.md
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@@ -27,3 +27,17 @@ Resulting in, e.g.
2024-04-01T18:25:48.295243016Z INFO No token / actor_name on disk, starting in signed-out state
2024-04-01T18:25:48.295360641Z INFO null
```
## Benchmarking on Linux
The recommended way for benchmarking any of the Rust components is Linux' `perf` utility.
For example, to attach to a running application, do:
1. Ensure the binary you are profiling is compiled with the `bench` profile.
1. `sudo perf perf record -g --freq 10000 --pid $(pgrep <your-binary>)`.
1. Run the speed test or whatever load-inducing task you want to measure.
1. `sudo perf script > profile.perf`
1. Open [profiler.firefox.com](https://profiler.firefox.com) and load `profile.perf`
Instead of attaching to a process with `--pid`, you can also specify the path to executable directly.
That is useful if you want to capture perf data for a test or a micro-benchmark.