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Bug 1906078 - Avoid pathological VecDeque behavior on parallel traversal. r=dshin, a=dmeehan

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Using split_off to split the front chunk from the queue seems like it'd
be efficient, but it's not:

  https://github.com/rust-lang/rust/issues/127281

Instead, pass the range of nodes to distribute, and use
VecDeque::from_iter in the callee. Then, just truncate() the queue to
the remaining local work.

Differential Revision: https://phabricator.services.mozilla.com/D215705
This commit is contained in:
Emilio Cobos Álvarez 2024-07-08 18:07:42 +00:00
parent e2f7fdc56e
commit e31ff5e9c6
1 changed files with 10 additions and 15 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

25
servo/components/style/parallel.rs
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@ -95,7 +95,7 @@ fn distribute_one_chunk<'a, 'scope, E, D>(
/// Distributes all items into the thread pool, in `work_unit_max` chunks. /// Distributes all items into the thread pool, in `work_unit_max` chunks.
fn distribute_work<'a, 'scope, E, D>( fn distribute_work<'a, 'scope, E, D>(
mut items: VecDeque<SendNode<E::ConcreteNode>>, mut items: impl Iterator<Item = SendNode<E::ConcreteNode>>,
traversal_root: OpaqueNode, traversal_root: OpaqueNode,
work_unit_max: usize, work_unit_max: usize,
traversal_data: PerLevelTraversalData, traversal_data: PerLevelTraversalData,
@ -106,10 +106,14 @@ fn distribute_work<'a, 'scope, E, D>(
E: TElement + 'scope, E: TElement + 'scope,
D: DomTraversal<E>, D: DomTraversal<E>,
{ {
while items.len() > work_unit_max { use std::iter::FromIterator;
let rest = items.split_off(work_unit_max); loop {
let chunk = VecDeque::from_iter(items.by_ref().take(work_unit_max));
if chunk.is_empty() {
return;
}
distribute_one_chunk( distribute_one_chunk(
items, chunk,
traversal_root, traversal_root,
work_unit_max, work_unit_max,
traversal_data, traversal_data,
@ -117,17 +121,7 @@ fn distribute_work<'a, 'scope, E, D>(
traversal, traversal,
tls, tls,
); );
items = rest;
} }
distribute_one_chunk(
items,
traversal_root,
work_unit_max,
traversal_data,
scope,
traversal,
tls,
);
} }
/// Processes `discovered` items, possibly spawning work in other threads as needed. /// Processes `discovered` items, possibly spawning work in other threads as needed.
@ -175,7 +169,7 @@ pub fn style_trees<'a, 'scope, E, D>(
let mut traversal_data_copy = traversal_data.clone(); let mut traversal_data_copy = traversal_data.clone();
traversal_data_copy.current_dom_depth += 1; traversal_data_copy.current_dom_depth += 1;
distribute_work( distribute_work(
discovered.split_off(kept_work), discovered.range(kept_work..).cloned(),
traversal_root, traversal_root,
work_unit_max, work_unit_max,
traversal_data_copy, traversal_data_copy,
@ -183,6 +177,7 @@ pub fn style_trees<'a, 'scope, E, D>(
traversal, traversal,
tls, tls,
); );
discovered.truncate(kept_work);
} }
if nodes_remaining_at_current_depth == 0 { if nodes_remaining_at_current_depth == 0 {