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Update build advice for benchmarking and profiling #22

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Sep 23, 2024
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Update build advice for benchmarking and profiling #22

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9ec1678
Profiling: update recommended build instructions
delan Sep 13, 2024
4f9680c
Building Servo: update production; add -stripped and profiling
delan Sep 20, 2024
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50 changes: 43 additions & 7 deletions src/hacking/building-servo.md
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Expand Up @@ -52,22 +52,58 @@ There are three main build profiles, which you can build and use independently o
<th>mach option
<td><code>-d</code>
<td><code>-r</code>
<td><code>--profile production</code>
<td><code>--prod</code>
<tr>
<th>optimised?
<td>no<td>yes<td>yes
<td><a href="https://doc.rust-lang.org/cargo/reference/profiles.html#dev">no</a>
<td><a href="https://github.com/servo/servo/blob/457d37d94ee6966cad377c373d333a00c637e1ae/Cargo.toml#L153">yes</a>
<td>yes, <a href="https://github.com/servo/servo/blob/457d37d94ee6966cad377c373d333a00c637e1ae/Cargo.toml#L159-L160">more</a> <a href="https://github.com/servo/servo/blob/457d37d94ee6966cad377c373d333a00c637e1ae/Cargo.toml#L170-L171">than</a> in <strong>release</strong>
<tr>
<th>debug info?
<td>yes<td>no<td>no
<th>maximum RUST_LOG level
<td><code>trace</code>
<td><code>info</code>
<td><code>info</code>
<tr>
<th>debug assertions?
<td>yes<td>yes(!)<td>no
<tr>
<th>maximum RUST_LOG level
<td><code>trace</code><td><code>info</code><td><code>info</code>
<th>debug info?
<td>yes<td>no<td>no
<tr>
<th>symbols?
<td>yes<td>no<td>yes
<tr>
<th>finds resources in<br>current working dir?
<td>yes<td>yes<td>no(!)
</table>

There are also two special variants of production builds for performance-related use cases:

- `production-stripped` builds are ideal for benchmarking Servo over time, with debug symbols stripped for faster initial startup
- `profiling` builds are ideal for [profiling](profiling.md) and troubleshooting performance issues; they behave like a debug or release build, but have the same performance as a production build

<table>
<thead>
<tr>
<th>
<th>production
<th>production-stripped
<th>profiling
<tbody>
<tr>
<th>mach <code>--profile</code>
<td><code>production</code>
<td><code>production-stripped</code>
<td><code>profiling</code>
<tr>
<th>debug info?
<td>no<td>no<td>yes
<tr>
<th>symbols?
<td>yes<td>no<td>yes
<tr>
<th>finds resources in<br>current working dir?
<td>yes<td>yes<td>no
<td>no<td>no<td>yes(!)
</table>

You can change these settings in a servobuild file (see [servobuild.example](https://github.com/servo/servo/blob/b79e2a0b6575364de01b1f89021aba0ec3fcf399/servobuild.example)) or in the root [Cargo.toml](https://github.com/servo/servo/blob/b79e2a0b6575364de01b1f89021aba0ec3fcf399/Cargo.toml).
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14 changes: 5 additions & 9 deletions src/hacking/profiling.md
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Expand Up @@ -2,18 +2,14 @@

# Profiling

First, ensure that you are building Servo in release (optimized) mode with optimal debugging symbols:
In Cargo.toml:
When profiling Servo or troubleshooting performance issues, make sure your build is optimised while still allowing for accurate profiling data.

```
[profile.release]
debug = true
lto = false
```sh
$ ./mach build --profile profiling --with-frame-pointer
```

```
./mach build --release --with-frame-pointers
```
- **--profile profiling** builds Servo with [our profiling configuration](building-servo.md#build-profiles)
- **--with-frame-pointer** builds Servo with stack frame pointers on all platforms

Several ways to get profiling information about Servo's runs:
* [Interval Profiling](#interval-profiling)
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