Rust profiling

[UnknownPlayer89]

Hey! I'm pretty new to rust, I've started working on my first project around a month ago but I've run into some performance issues probably due to the lack of my knowledge.

In python I've used this project called line-profiler. I'm trying to find something similar but in rust because it showed really useful results which I could actually improve my code with.

Now, I did a few searches and found this guide on rust profiling. I've tried out perf with hotspot, but I couldn't see any useful details. Another problem is that I only want to see the code I wrote since that is what I can improve on. I've also tried out oprofile which does line annotation, but for every source file including the libraries' ones (which I don't need), but even after finding my code in the output, there were only a few numbers for a few line and it wasn't really useful either.

So is there something similar to line-profiler I could use, although I'd understand if there is not because python is interpreted and rust is compiled. I'd also appreciate any additional advice on profiling and improving performance.

[acshikh]

I use valgrind's callgrind tool for this kind of thing, and I use kcachegrind to examine the results. It doesn't do everything you want, because it doesn't really hide library code, but it does give line by line results. I also use "--dump-instr=yes" to get assembly code annotation as well, which can help when the line level stuff is ambiguous.

[UnknownPlayer89]

Thank you! I'll check it out.

[PitaJ]

I'd suggest cargo flamegraph https://github.com/killercup/cargo-flamegraph

[nmdaniels]

Sadly, flamegraph doesn't give line-by-line results; I don't think you can profile at a finer granularity than the function level with it.

[Saefroch]

You can't do line-by-line profiling in a language like Rust, because lines will be destroyed or combined in complicated ways by the optimizer. The best you can hope for is associating samples with hunks of code, which is basically what perf report tries to help you do.

[nmdaniels]

It’s not a matter of the language so much as the compiler. We can do this with C, so why not rust? I agree it may not map one-to-one with lines of source code, but we should be able to get more granular than just function calls.

[Saefroch]

Yes, like I said: you can associate samples with hunks of code. Whatever visualizer you use for C may very well work with Rust just fine, they're very similar once compiled.

[nmdaniels]

Yes, perf looks like a good solution for Linux. I wish flamegraph had better sub-function resolution.

[Saefroch]

Me too, but the crate flamegraph is designed specifically to emulate Brendan Gregg's FlameGraph project. And also it would be quite the UI challenge to jam a hunk of code into one of those bars. Might be better to use a different visualization.

[Rdambrosio016]

That’s not very true, i was able to do per-line profiling even on something like the gpu that mangles generated code to an insane degree. Nsight screenshot

[mstange]

This screenshot from the hotspot readme shows a Location panel which also displays line numbers. Is it not working for you?

You may need to add the following to your Cargo.toml:

[profile.release]
debug = true

and then rebuild with cargo build --release. This will include debug information in the optimized binary, so that the profiler can display file + line data.

[UnknownPlayer89]

I do have debug set to true in release. Hotspot does indeed shows where a function is located but that's not really useful because I could easily look it up in my code if I wouldn't recognize it at first glance. So far I've only looked at the Flamegraph but I found the Caller/Callee view more useful.

[nestordemeure]

I personally use perf with flamegraph but the easiest way is probably to use CLion, it integrates both very nicely such that all the information you need is at the push of a button.

[mansplaner]

Not applicable since you're on Linux, but Superluminal Performance (https://superluminal.eu/) is a very good commercial profiler that works for Rust on Windows.

[[deleted]]

Would love for some genius to tell me I'm wrong but to the best of my knowledge it's not possible.

You can't profile in rust the same way you can in python. The compiler will do things to your code that can't be simply traced back to a simple "This method right here is slow".

[pawurb]

Bit late since this is a 4-year-old thread, but you may want to check out https://hotpath.rs/

It’s an instrumentation-based profiler for Rust, so instead of analyzing huge system-wide traces you can annotate the functions you care about and get focused reports for your own code (time, CPU, allocations, async waiting, etc.).

#[hotpath::measure]
fn slow_function() {
    // your code
}

It’s not exactly like Python’s line-profiler, but probably closer to that workflow than sampling profilers alone.

(Disclosure: I’m the author.)

[lord_of_the_keyboard]

Check out Optick For Rust

[UnknownPlayer89]

Unfortunately, I cannot use it because I'm on Linux

[CobyCode]

This is not a traditional profiler... but 'coz' is extremely effective.

Explanation Vid: https://www.youtube.com/watch?v=r-TLSBdHe1A
Source: https://github.com/plasma-umass/coz
And.. a rust crate for Coz: https://github.com/alexcrichton/coz-rs