From 6995e60ee159f3a0c7c6cacbdb7961fe23f68877 Mon Sep 17 00:00:00 2001
From: Shubham Gupta <32428749+shubhamg13@users.noreply.github.com>
Date: Tue, 30 Sep 2025 19:07:35 +0800
Subject: [PATCH] compositor: Add Paint Metric events to Perfetto Traces
 (#39502)

> Some metrics like TimeToFirstPaint and TimeToFirstContentfulPaint are
only in the HTML traces. [See
this](https://github.com/servo/perf-analysis-tools?tab=readme-ov-file#how-to-analyse-a-single-servo-sample)

In order to analyse the performance and refine
[perf-analysis-tools](https://github.com/servo/perf-analysis-tools) we
need these metrics to be added to Perfetto also.

<img width="993" height="359" alt="Screenshot from 2025-09-26 15-00-00"
src="https://github.com/user-attachments/assets/9755f344-a98e-4671-b347-d76cd6311afe"
/>

<img width="1186" height="359" alt="Screenshot from 2025-09-26 15-00-42"
src="https://github.com/user-attachments/assets/a25e3a5f-eef0-45b7-be69-5de919bfb663"
/>

Testing: Verified by using Perfetto traces

Signed-off-by: Shubham Gupta <shubham.gupta@chromium.org>
---
 components/compositing/compositor.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 12c80f29be1..fb67ca41a2c 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -1383,6 +1383,14 @@ impl IOCompositor {
                     // the first "real" display list.
                     PaintMetricState::Seen(epoch, first_reflow) if epoch <= current_epoch => {
                         assert!(epoch <= current_epoch);
+                        #[cfg(feature = "tracing")]
+                        tracing::info!(
+                            name: "FirstPaint",
+                            servo_profiling = true,
+                            epoch = ?epoch,
+                            paint_time = ?paint_time,
+                            pipeline_id = ?pipeline_id,
+                        );
                         if let Err(error) = self.global.borrow().constellation_sender.send(
                             EmbedderToConstellationMessage::PaintMetric(
                                 *pipeline_id,
@@ -1400,6 +1408,14 @@ impl IOCompositor {
 
                 match pipeline.first_contentful_paint_metric {
                     PaintMetricState::Seen(epoch, first_reflow) if epoch <= current_epoch => {
+                        #[cfg(feature = "tracing")]
+                        tracing::info!(
+                            name: "FirstContentfulPaint",
+                            servo_profiling = true,
+                            epoch = ?epoch,
+                            paint_time = ?paint_time,
+                            pipeline_id = ?pipeline_id,
+                        );
                         if let Err(error) = self.global.borrow().constellation_sender.send(
                             EmbedderToConstellationMessage::PaintMetric(
                                 *pipeline_id,