layout: Improve and expand category names for layout profiling (#37833)

This improves naming of layout categories and adds tracing for each
layout phase.

Testing: This just adds / adjusts profiling categories, so doesn't need
tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/layout/flow/root.rs

@@ -45,6 +45,7 @@ pub struct BoxTree {
 }
 
 impl BoxTree {
+    #[servo_tracing::instrument(name = "Box Tree Construction", skip_all)]
     pub(crate) fn construct(context: &LayoutContext, root_element: ServoLayoutNode<'_>) -> Self {
         let boxes = construct_for_root_element(context, root_element);
 
@@ -191,6 +192,7 @@ fn construct_for_root_element(
 }
 
 impl BoxTree {
+    #[servo_tracing::instrument(name = "Fragment Tree Construction", skip_all)]
     pub(crate) fn layout(
         &self,
         layout_context: &LayoutContext,

components/layout/layout_impl.rs

@@ -440,7 +440,7 @@ impl Layout for LayoutThread {
 
     fn reflow(&mut self, reflow_request: ReflowRequest) -> Option<ReflowResult> {
         time_profile!(
-            profile_time::ProfilerCategory::LayoutPerform,
+            profile_time::ProfilerCategory::Layout,
             self.profiler_metadata(),
             self.time_profiler_chan.clone(),
             || self.handle_reflow(reflow_request),
@@ -821,27 +821,34 @@ impl LayoutThread {
             .restyle
             .as_ref()
             .expect("Should not get here if there is not restyle.");
-        let dirty_root = unsafe {
-            ServoLayoutNode::new(&restyle.dirty_root.unwrap())
-                .as_element()
-                .unwrap()
-        };
 
-        let recalc_style_traversal = RecalcStyle::new(&layout_context);
-        let token = {
-            let shared =
-                DomTraversal::<ServoLayoutElement>::shared_context(&recalc_style_traversal);
-            RecalcStyle::pre_traverse(dirty_root, shared)
-        };
+        let recalc_style_traversal;
+        let dirty_root;
+        {
+            #[cfg(feature = "tracing")]
+            let _span = tracing::trace_span!("Styling", servo_profiling = true).entered();
 
-        if !token.should_traverse() {
-            layout_context.style_context.stylist.rule_tree().maybe_gc();
-            return (RestyleDamage::empty(), IFrameSizes::default());
+            let original_dirty_root = unsafe {
+                ServoLayoutNode::new(&restyle.dirty_root.unwrap())
+                    .as_element()
+                    .unwrap()
+            };
+
+            recalc_style_traversal = RecalcStyle::new(&layout_context);
+            let token = {
+                let shared =
+                    DomTraversal::<ServoLayoutElement>::shared_context(&recalc_style_traversal);
+                RecalcStyle::pre_traverse(original_dirty_root, shared)
+            };
+
+            if !token.should_traverse() {
+                layout_context.style_context.stylist.rule_tree().maybe_gc();
+                return (RestyleDamage::empty(), IFrameSizes::default());
+            }
+
+            dirty_root = driver::traverse_dom(&recalc_style_traversal, token, rayon_pool).as_node();
         }
 
-        let dirty_root: ServoLayoutNode =
-            driver::traverse_dom(&recalc_style_traversal, token, rayon_pool).as_node();
-
         let root_node = root_element.as_node();
         let mut damage = compute_damage_and_repair_style(&layout_context.style_context, root_node);
         if viewport_changed {
@@ -909,6 +916,7 @@ impl LayoutThread {
         (damage, std::mem::take(&mut *iframe_sizes))
     }
 
+    #[servo_tracing::instrument(name = "Overflow Calculation", skip_all)]
     fn calculate_overflow(&self, damage: RestyleDamage) {
         if !damage.contains(RestyleDamage::RECALCULATE_OVERFLOW) {
             return;
@@ -927,6 +935,7 @@ impl LayoutThread {
         self.need_new_stacking_context_tree.set(true);
     }
 
+    #[servo_tracing::instrument(name = "Stacking Context Tree Construction", skip_all)]
     fn build_stacking_context_tree(&self, reflow_request: &ReflowRequest, damage: RestyleDamage) {
         if !ReflowPhases::necessary(&reflow_request.reflow_goal)
             .contains(ReflowPhases::StackingContextTreeConstruction)
@@ -999,6 +1008,7 @@ impl LayoutThread {
 
     /// Build the display list for the current layout and send it to the renderer. If no display
     /// list is built, returns false.
+    #[servo_tracing::instrument(name = "Display List Construction", skip_all)]
     fn build_display_list(
         &self,
         reflow_request: &ReflowRequest,

components/layout/traversal.rs

@@ -92,6 +92,7 @@ where
     }
 }
 
+#[servo_tracing::instrument(skip_all)]
 pub(crate) fn compute_damage_and_repair_style(
     context: &SharedStyleContext,
     node: ServoLayoutNode<'_>,

components/shared/profile/time.rs

@@ -66,7 +66,7 @@ pub enum ProfilerCategory {
     Compositing = 0x00,
 
     /// The script thread is doing layout work.
-    LayoutPerform = 0x10,
+    Layout = 0x10,
 
     ImageSaving = 0x51,
     ScriptAttachLayout = 0x60,
@@ -126,7 +126,7 @@ impl ProfilerCategory {
     pub const fn variant_name(&self) -> &'static str {
         match self {
             ProfilerCategory::Compositing => "Compositing",
-            ProfilerCategory::LayoutPerform => "LayoutPerform",
+            ProfilerCategory::Layout => "Layout",
             ProfilerCategory::ImageSaving => "ImageSaving",
             ProfilerCategory::ScriptAttachLayout => "ScriptAttachLayout",
             ProfilerCategory::ScriptConstellationMsg => "ScriptConstellationMsg",