Profiling: update recommended build instructions

Author: delan

src/hacking/building-servo.md

@@ -47,27 +47,32 @@ There are three main build profiles, which you can build and use independently o
         <th>debug
         <th>release
         <th>production
+        <th>profiling
 <tbody>
     <tr>
         <th>mach option
         <td><code>-d</code>
         <td><code>-r</code>
         <td><code>--profile production</code>
+        <td><code>--profile profiling</code>
     <tr>
         <th>optimised?
-        <td>no<td>yes<td>yes
+        <td>no<td>yes<td>yes (with LTO)<td>yes
     <tr>
         <th>debug info?
-        <td>yes<td>no<td>no
+        <td>yes<td>no<td>no<td>yes
     <tr>
         <th>debug assertions?
-        <td>yes<td>yes(!)<td>no
+        <td>yes<td>yes(!)<td>no<td>no
     <tr>
         <th>maximum RUST_LOG level
-        <td><code>trace</code><td><code>info</code><td><code>info</code>
+        <td><code>trace</code>
+        <td><code>info</code>
+        <td><code>info</code>
+        <td><code>info</code>
     <tr>
         <th>finds resources in<br>current working dir?
-        <td>yes<td>yes<td>no
+        <td>yes<td>yes<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).

src/hacking/profiling.md

@@ -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 measuring its performance, make sure your build is optimised in a way that still allows 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](http://localhost:3000/hacking/building-servo.html#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)