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util: Reduce memory barriers and integer divisions in the work queue.

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Improves scaling on multicore ARM devices.
This commit is contained in:
Patrick Walton 2015-06-11 15:07:16 -07:00
parent d87af8ac52
commit a063fdde73
2 changed files with 50 additions and 31 deletions
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21
components/util/deque/mod.rs
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@ -45,8 +45,7 @@
// NB: the "buffer pool" strategy is not done for speed, but rather for
// correctness. For more info, see the comment on `swap_buffer`
// FIXME: all atomic operations in this module use a SeqCst ordering. That is
// probably overkill
// FIXME: more than likely, more atomic operations than necessary use SeqCst
pub use self::Stolen::{Empty, Abort, Data};
@ -58,7 +57,7 @@ use std::ptr;
use std::sync::Mutex;
use std::sync::atomic::{AtomicIsize, AtomicPtr};
use std::sync::atomic::Ordering::SeqCst;
use std::sync::atomic::Ordering::{Relaxed, SeqCst};
// Once the queue is less than 1/K full, then it will be downsized. Note that
// the deque requires that this number be less than 2.
@ -240,8 +239,8 @@ impl<T: Send + 'static> Deque<T> {
}
unsafe fn push(&self, data: T) {
let mut b = self.bottom.load(SeqCst);
let t = self.top.load(SeqCst);
let mut b = self.bottom.load(Relaxed);
let t = self.top.load(Relaxed);
let mut a = self.array.load(SeqCst);
let size = b - t;
if size >= (*a).size() - 1 {
@ -256,11 +255,11 @@ impl<T: Send + 'static> Deque<T> {
}
unsafe fn pop(&self) -> Option<T> {
let b = self.bottom.load(SeqCst);
let b = self.bottom.load(Relaxed);
let a = self.array.load(SeqCst);
let b = b - 1;
self.bottom.store(b, SeqCst);
let t = self.top.load(SeqCst);
let t = self.top.load(Relaxed);
let size = b - t;
if size < 0 {
self.bottom.store(t, SeqCst);
@ -282,12 +281,12 @@ impl<T: Send + 'static> Deque<T> {
}
unsafe fn steal(&self) -> Stolen<T> {
let t = self.top.load(SeqCst);
let old = self.array.load(SeqCst);
let b = self.bottom.load(SeqCst);
let a = self.array.load(SeqCst);
let t = self.top.load(Relaxed);
let old = self.array.load(Relaxed);
let b = self.bottom.load(Relaxed);
let size = b - t;
if size <= 0 { return Empty }
let a = self.array.load(SeqCst);
if size % (*a).size() == 0 {
if a == old && t == self.top.load(SeqCst) {
return Empty