Acquire wq locks only if there might be something to do

7228e39c · Silas Boyd-Wickizer · d7407c57 · 7228e39c
--- a/wq.cc
+++ b/wq.cc
@@ -118,6 +118,10 @@ __wq_pop(int c)
  struct wqueue *wq = &queue[c];
  struct work *w;
  int i;
+  i = wq->head;
+  if ((i - wq->tail) == 0)
+    return 0;
  acquire(&wq->lock);
  i = wq->head;
@@ -142,7 +146,8 @@ __wq_steal(int c)
  struct work *w;
  int i;
-  acquire(&wq->lock);
+  if (tryacquire(&wq->lock) == 0)
+    return 0;
  i = wq->tail;
  if ((i - wq->head) == 0) {
    release(&wq->lock);