---
title: "Profiling Rust NIFs in Elixir"
url: https://daily.dev/posts/profiling-rust-nifs-in-elixir-7eg5wsgft
source_url: https://blog.smaller-infinity.com/posts/profiling-rust-nifs-in-elixir
type: article
source: "Awesome Elixir"
published: 2026-08-06T20:08:10.706Z
updated: 2026-08-06T20:08:47.104Z
tags: ["rust", "elixir"]
reading_time: 12
upvotes: 0
comments: 0
language: en
---

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# Profiling Rust NIFs in Elixir

**[Awesome Elixir](https://daily.dev/sources/awelix)** · 12 min read · 0 upvotes · 0 comments

## Summary

A practical guide to profiling Rust NIFs (Native Implemented Functions) called from Elixir, using the `hotpath` crate alongside Rustler and Benchee. The post walks through setting up a small Elixir/Rust project, configuring `hotpath` as an optional Cargo feature, wiring up the profiler lifecycle via Rustler's `on_load` hook and a custom NIF to flush results, and collecting per-function timing and allocation data into JSON. The resulting profile output reveals that `first_thing` is responsible for all allocations and most CPU time, demonstrating how to identify optimization targets across the language boundary.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://blog.smaller-infinity.com/posts/profiling-rust-nifs-in-elixir>

## Questions this post answers

### How do I profile Rust NIF functions called from Elixir to get per-function timing and allocation data?

Use the `hotpath` crate as an optional Cargo feature alongside Rustler. Mark functions with `#[cfg_attr(feature = "hotpath", hotpath::measure)]`, initialize a `HotpathGuard` in Rustler's `on_load` hook stored in a static Mutex, and expose a `hotpath_finish` NIF that drops the guard to flush results to JSON. Pass the feature flags at compile time via an environment variable read by the Rustler `use` macro.

_Developers bridging Rust and Elixir for performance track NIF profiling techniques like this on daily.dev._

### How do I pass Cargo features to a Rustler crate conditionally at compile time from Elixir?

Read an environment variable at compile time inside the Elixir module that calls `use Rustler`, assign it to a module attribute, and pass it as the `features:` option. Because module attributes and `use` macros are evaluated at compile time, running `mix compile --force` with the environment variable set causes Rustler to forward the feature flags to Cargo, enabling or disabling optional dependencies like `hotpath`.

_Elixir teams shipping Rust NIFs find compile-time configuration patterns like this discussed on daily.dev._

---

Tags: [#rust](https://daily.dev/tags/rust), [#elixir](https://daily.dev/tags/elixir)

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