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Increase the size of the style sharing cache to 31.
Still a lot of guesswork here, but this does seem to get us better sharing. See https://bugzilla.mozilla.org/show_bug.cgi?id=1369621 for some data.
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2 changed files with 12 additions and 16 deletions
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@ -26,7 +26,6 @@ use context::TraversalStatistics;
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use dom::{OpaqueNode, SendNode, TElement, TNode};
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use rayon;
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use scoped_tls::ScopedTLS;
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use sharing::STYLE_SHARING_CANDIDATE_CACHE_SIZE;
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use smallvec::SmallVec;
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use std::borrow::Borrow;
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use std::mem;
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@ -36,21 +35,10 @@ use traversal::{DomTraversal, PerLevelTraversalData, PreTraverseToken};
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/// The maximum number of child nodes that we will process as a single unit.
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///
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/// Larger values will increase style sharing cache hits and general DOM locality
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/// at the expense of decreased opportunities for parallelism. The style sharing
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/// cache can hold 8 entries, but not all styles are shareable, so we set this
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/// value to 16. These values have not been measured and could potentially be
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/// tuned.
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/// at the expense of decreased opportunities for parallelism. This value has not
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/// been measured and could potentially be tuned.
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pub const WORK_UNIT_MAX: usize = 16;
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/// Verify that the style sharing cache size doesn't change. If it does, we should
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/// reconsider the above. We do this, rather than defining WORK_UNIT_MAX in terms
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/// of STYLE_SHARING_CANDIDATE_CACHE_SIZE, so that altering the latter doesn't
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/// have surprising effects on the parallelism characteristics of the style system.
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#[allow(dead_code)]
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fn static_assert() {
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unsafe { mem::transmute::<_, [u32; STYLE_SHARING_CANDIDATE_CACHE_SIZE]>([1; 8]); }
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}
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/// A list of node pointers.
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///
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/// Note that the inline storage doesn't need to be sized to WORK_UNIT_MAX, but
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@ -84,8 +84,16 @@ use stylist::{ApplicableDeclarationBlock, Stylist};
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mod checks;
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/// The amount of nodes that the style sharing candidate cache should hold at
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/// most.
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pub const STYLE_SHARING_CANDIDATE_CACHE_SIZE: usize = 8;
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/// most. We'd somewhat like 32, but ArrayDeque only implements certain backing
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/// store sizes. A cache size of 32 would mean a backing store of 33, but
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/// that's not an implemented size: we can do 32 or 40.
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///
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/// The cache size was chosen by measuring style sharing and resulting
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/// performance on a few pages; sizes up to about 32 were giving good sharing
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/// improvements (e.g. 3x fewer styles having to be resolved than at size 8) and
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/// slight performance improvements. Sizes larger than 32 haven't really been
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/// tested.
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pub const STYLE_SHARING_CANDIDATE_CACHE_SIZE: usize = 31;
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/// Controls whether the style sharing cache is used.
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#[derive(Clone, Copy, PartialEq)]
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