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layout: Disable parallel display list building by default.

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I've never see it result in a speedup. Actually, I don't think I've seen
it result in anything better than a 50% slowdown. The arithmetic
intensity is just too low, at least with the current algorithm.

Parallel DL building can still be enabled with a debug flag if the
algorithm is improved.
This commit is contained in:
Patrick Walton 2015-06-12 17:47:50 -07:00
parent 836ac8a0b6
commit eef9c5d9bf
2 changed files with 12 additions and 6 deletions
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12
components/layout/layout_task.rs
View file

@ -821,18 +821,18 @@ impl LayoutTask {
flow::mut_base(&mut **layout_root).clip = flow::mut_base(&mut **layout_root).clip =
ClippingRegion::from_rect(&data.page_clip_rect); ClippingRegion::from_rect(&data.page_clip_rect);
match rw_data.parallel_traversal { match (&mut rw_data.parallel_traversal, opts::get().parallel_display_list_building) {
None => { (&mut Some(ref mut traversal), true) => {
sequential::build_display_list_for_subtree(layout_root,
shared_layout_context);
}
Some(ref mut traversal) => {
parallel::build_display_list_for_subtree(layout_root, parallel::build_display_list_for_subtree(layout_root,
self.profiler_metadata(), self.profiler_metadata(),
self.time_profiler_chan.clone(), self.time_profiler_chan.clone(),
shared_layout_context, shared_layout_context,
traversal); traversal);
} }
_ => {
sequential::build_display_list_for_subtree(layout_root,
shared_layout_context);
}
} }
if data.goal == ReflowGoal::ForDisplay { if data.goal == ReflowGoal::ForDisplay {

6
components/util/opts.rs
View file

@ -152,6 +152,9 @@ pub struct Opts {
/// Whether Style Sharing Cache is used /// Whether Style Sharing Cache is used
pub disable_share_style_cache: bool, pub disable_share_style_cache: bool,
/// Whether to run absolute position calculation and display list construction in parallel.
pub parallel_display_list_building: bool,
} }
fn print_usage(app: &str, opts: &[getopts::OptGroup]) { fn print_usage(app: &str, opts: &[getopts::OptGroup]) {
@ -183,6 +186,7 @@ pub fn print_debug_usage(app: &str) {
"Display an error when display list geometry escapes overflow region."); "Display an error when display list geometry escapes overflow region.");
print_option("disable-share-style-cache", print_option("disable-share-style-cache",
"Disable the style sharing cache."); "Disable the style sharing cache.");
print_option("parallel-display-list-building", "Build display lists in parallel.");
println!(""); println!("");
} }
@ -241,6 +245,7 @@ pub fn default_opts() -> Opts {
resources_path: None, resources_path: None,
sniff_mime_types: false, sniff_mime_types: false,
disable_share_style_cache: false, disable_share_style_cache: false,
parallel_display_list_building: false,
} }
} }
@ -420,6 +425,7 @@ pub fn from_cmdline_args(args: &[String]) -> bool {
resources_path: opt_match.opt_str("resources-path"), resources_path: opt_match.opt_str("resources-path"),
sniff_mime_types: opt_match.opt_present("sniff-mime-types"), sniff_mime_types: opt_match.opt_present("sniff-mime-types"),
disable_share_style_cache: debug_options.contains(&"disable-share-style-cache"), disable_share_style_cache: debug_options.contains(&"disable-share-style-cache"),
parallel_display_list_building: debug_options.contains(&"parallel-display-list-building"),
}; };
set(opts); set(opts);