Auto merge of #19549 - Manishearth:telemetry, r=emilio

Add telemetry probe for measuring frequency of parallel restyles

Servo side of https://bugzilla.mozilla.org/show_bug.cgi?id=1421195

r=emilio

components/style/context.rs

@@ -116,6 +116,21 @@ impl Default for StyleSystemOptions {
     }
 }
 
+impl StyleSystemOptions {
+    #[cfg(feature = "servo")]
+    /// On Gecko's nightly build?
+    pub fn is_nightly(&self) -> bool {
+        false
+    }
+
+    #[cfg(feature = "gecko")]
+    /// On Gecko's nightly build?
+    #[inline]
+    pub fn is_nightly(&self) -> bool {
+        structs::GECKO_IS_NIGHTLY
+    }
+}
+
 /// A shared style context.
 ///
 /// There's exactly one of these during a given restyle traversal, and it's

components/style/driver.rs

@@ -7,7 +7,7 @@
 
 #![deny(missing_docs)]
 
-use context::{StyleContext, ThreadLocalStyleContext};
+use context::{StyleContext, ThreadLocalStyleContext, TraversalStatistics};
 use dom::{SendNode, TElement, TNode};
 use parallel;
 use parallel::{DispatchMode, WORK_UNIT_MAX};
@@ -25,11 +25,15 @@ use traversal::{DomTraversal, PerLevelTraversalData, PreTraverseToken};
 /// processing, until we arrive at a wide enough level in the DOM that the
 /// parallel traversal would parallelize it. If a thread pool is provided, we
 /// then transfer control over to the parallel traversal.
+///
+/// Returns true if the traversal was parallel, and also returns the statistics
+/// object containing information on nodes traversed (on nightly only). Not
+/// all of its fields will be initialized since we don't call finish().
 pub fn traverse_dom<E, D>(
     traversal: &D,
     token: PreTraverseToken<E>,
     pool: Option<&rayon::ThreadPool>
-)
+) -> (bool, Option<TraversalStatistics>)
 where
     E: TElement,
     D: DomTraversal<E>,
@@ -38,6 +42,8 @@ where
         token.traversal_root().expect("Should've ensured we needed to traverse");
 
     let dump_stats = traversal.shared_context().options.dump_style_statistics;
+    let is_nightly  = traversal.shared_context().options.is_nightly();
+    let mut used_parallel = false;
     let start_time = if dump_stats { Some(time::precise_time_s()) } else { None };
 
     // Declare the main-thread context, as well as the worker-thread contexts,
@@ -84,6 +90,7 @@ where
             // moving to the next level in the dom so that we can pass the same
             // depth for all the children.
             if pool.is_some() && discovered.len() > WORK_UNIT_MAX {
+                used_parallel = true;
                 let pool = pool.unwrap();
                 maybe_tls = Some(ScopedTLS::<ThreadLocalStyleContext<E>>::new(pool));
                 let root_opaque = root.as_node().opaque();
@@ -108,9 +115,9 @@ where
             nodes_remaining_at_current_depth = discovered.len();
         }
     }
-
-    // Dump statistics to stdout if requested.
-    if dump_stats {
+    let mut maybe_stats = None;
+    // Accumulate statistics
+    if dump_stats || is_nightly {
         let mut aggregate =
             mem::replace(&mut context.thread_local.statistics, Default::default());
         let parallel = maybe_tls.is_some();
@@ -123,9 +130,14 @@ where
                 }
             });
         }
-        aggregate.finish(traversal, parallel, start_time.unwrap());
-        if aggregate.is_large_traversal() {
-            println!("{}", aggregate);
+
+        // dump to stdout if requested
+        if dump_stats && aggregate.is_large_traversal() {
+            aggregate.finish(traversal, parallel, start_time.unwrap());
+             println!("{}", aggregate);
         }
+        maybe_stats = Some(aggregate);
     }
+
+    (used_parallel, maybe_stats)
 }

components/style/gecko/data.rs

@@ -5,6 +5,7 @@
 //! Data needed to style a Gecko document.
 
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use context::TraversalStatistics;
 use dom::TElement;
 use gecko_bindings::bindings::{self, RawServoStyleSet};
 use gecko_bindings::structs::{RawGeckoPresContextOwned, ServoStyleSetSizes, ServoStyleSheet};
@@ -16,6 +17,7 @@ use media_queries::{Device, MediaList};
 use properties::ComputedValues;
 use servo_arc::Arc;
 use shared_lock::{Locked, StylesheetGuards, SharedRwLockReadGuard};
+use std::sync::atomic::{AtomicUsize, Ordering};
 use stylesheets::{StylesheetContents, StylesheetInDocument};
 use stylist::Stylist;
 
@@ -107,11 +109,40 @@ impl StylesheetInDocument for GeckoStyleSheet {
     }
 }
 
+#[derive(Default)]
+/// Helper struct for counting traversals
+pub struct TraversalCount {
+    /// Total number of events
+    pub total_count: AtomicUsize,
+    /// Number of events which were parallel
+    pub parallel_count: AtomicUsize
+}
+
+impl TraversalCount {
+    fn record(&self, parallel: bool, count: u32) {
+        self.total_count.fetch_add(count as usize, Ordering::Relaxed);
+        if parallel {
+            self.parallel_count.fetch_add(count as usize, Ordering::Relaxed);
+        }
+    }
+
+    fn get(&self) -> (u32, u32) {
+        (self.total_count.load(Ordering::Relaxed) as u32,
+         self.parallel_count.load(Ordering::Relaxed) as u32)
+    }
+}
+
 /// The container for data that a Servo-backed Gecko document needs to style
 /// itself.
 pub struct PerDocumentStyleDataImpl {
     /// Rule processor.
     pub stylist: Stylist,
+    /// Counter for traversals that could have been parallel, for telemetry
+    pub traversal_count: TraversalCount,
+    /// Counter for traversals, weighted by elements traversed,
+    pub traversal_count_traversed: TraversalCount,
+    /// Counter for traversals, weighted by elements styled,
+    pub traversal_count_styled: TraversalCount,
 }
 
 /// The data itself is an `AtomicRefCell`, which guarantees the proper semantics
@@ -133,6 +164,9 @@ impl PerDocumentStyleData {
 
         PerDocumentStyleData(AtomicRefCell::new(PerDocumentStyleDataImpl {
             stylist: Stylist::new(device, quirks_mode.into()),
+            traversal_count: Default::default(),
+            traversal_count_traversed: Default::default(),
+            traversal_count_styled: Default::default(),
         }))
     }
 
@@ -147,6 +181,21 @@ impl PerDocumentStyleData {
     }
 }
 
+impl Drop for PerDocumentStyleDataImpl {
+    fn drop(&mut self) {
+        if !structs::GECKO_IS_NIGHTLY {
+            return
+        }
+        let (total, parallel)  = self.traversal_count.get();
+        let (total_t, parallel_t)  = self.traversal_count_traversed.get();
+        let (total_s, parallel_s)  = self.traversal_count_styled.get();
+
+        unsafe { bindings::Gecko_RecordTraversalStatistics(total, parallel,
+                                                           total_t, parallel_t,
+                                                           total_s, parallel_s) }
+    }
+}
+
 impl PerDocumentStyleDataImpl {
     /// Recreate the style data if the stylesheets have changed.
     pub fn flush_stylesheets<E>(
@@ -209,6 +258,15 @@ impl PerDocumentStyleDataImpl {
     pub fn add_size_of(&self, ops: &mut MallocSizeOfOps, sizes: &mut ServoStyleSetSizes) {
         self.stylist.add_size_of(ops, sizes);
     }
+
+    /// Record that a traversal happened for later collection as telemetry
+    pub fn record_traversal(&self, was_parallel: bool, stats: Option<TraversalStatistics>) {
+        self.traversal_count.record(was_parallel, 1);
+        if let Some(stats) = stats {
+            self.traversal_count_traversed.record(was_parallel, stats.elements_traversed);
+            self.traversal_count_styled.record(was_parallel, stats.elements_styled);
+        }
+    }
 }
 
 unsafe impl HasFFI for PerDocumentStyleData {

components/style/gecko/generated/bindings.rs

@@ -499,6 +499,8 @@ extern "C" {
  pub fn Servo_SelectorList_Drop ( ptr : RawServoSelectorListOwned , ) ; 
 } extern "C" {
  pub fn Servo_SourceSizeList_Drop ( ptr : RawServoSourceSizeListOwned , ) ; 
+} extern "C" {
+ pub fn Gecko_RecordTraversalStatistics ( total : u32 , parallel : u32 , total_t : u32 , parallel_t : u32 , total_s : u32 , parallel_s : u32 , ) ; 
 } extern "C" {
  pub fn Gecko_IsInDocument ( node : RawGeckoNodeBorrowed , ) -> bool ; 
 } extern "C" {

ports/geckolib/glue.rs

@@ -267,8 +267,19 @@ fn traverse_subtree(
         None
     };
 
+    let is_restyle = element.get_data().is_some();
+
     let traversal = RecalcStyleOnly::new(shared_style_context);
-    driver::traverse_dom(&traversal, token, thread_pool);
+    let (used_parallel, stats) = driver::traverse_dom(&traversal, token, thread_pool);
+
+    if traversal_flags.contains(TraversalFlags::ParallelTraversal) &&
+       !traversal_flags.contains(TraversalFlags::AnimationOnly) &&
+       is_restyle && !element.is_native_anonymous() {
+       // We turn off parallel traversal for background tabs; this
+       // shouldn't count in telemetry. We're also focusing on restyles so
+       // we ensure that it's a restyle.
+       per_doc_data.record_traversal(used_parallel, stats);
+    }
 }
 
 /// Traverses the subtree rooted at `root` for restyling.