semaphore: make test time independent of GOMAXPROCS

TestWeighted's runtime was roughly proportional to the number of CPUs,
so it ran a long time on PPCs (160 CPUs).

Make the number of loops in the test an inverse function of the number
of CPUs, to keep the test short.

Change-Id: Id853dbb5e5e2f9fb95966d19ef0c511e3f8080e0
Reviewed-on: https://go-review.googlesource.com/43632
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Author: jba

semaphore/semaphore_test.go

@@ -29,14 +29,15 @@ func TestWeighted(t *testing.T) {
 	t.Parallel()
 
 	n := runtime.GOMAXPROCS(0)
+	loops := 10000 / n
 	sem := NewWeighted(int64(n))
 	var wg sync.WaitGroup
 	wg.Add(n)
 	for i := 0; i < n; i++ {
 		i := i
 		go func() {
 			defer wg.Done()
-			HammerWeighted(sem, int64(i), 1000)
+			HammerWeighted(sem, int64(i), loops)
 		}()
 	}
 	wg.Wait()