runtime: make new tests shorter in short mode

We see timeouts in these tests on some platforms,
but not on the others.  The hypothesis is that
the problematic platforms are slow uniprocessors.
Stack traces do not suggest that the process
is completely hang, and it is able to schedule
the alarm goroutine. And if it actually hangs,
we still will be able to detect that.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/12253043

src/pkg/runtime/proc_test.go

@@ -94,9 +94,14 @@ func TestYieldLocked(t *testing.T) {
 }
 
 func TestGoroutineParallelism(t *testing.T) {
-	const P = 4
+	P := 4
+	N := 10
+	if testing.Short() {
+		P = 3
+		N = 3
+	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(P))
-	for try := 0; try < 10; try++ {
+	for try := 0; try < N; try++ {
 		done := make(chan bool)
 		x := uint32(0)
 		for p := 0; p < P; p++ {
@@ -194,7 +199,10 @@ var preempt = func() int {
 
 func TestPreemption(t *testing.T) {
 	// Test that goroutines are preempted at function calls.
-	const N = 5
+	N := 5
+	if testing.Short() {
+		N = 2
+	}
 	c := make(chan bool)
 	var x uint32
 	for g := 0; g < 2; g++ {
@@ -214,7 +222,12 @@ func TestPreemption(t *testing.T) {
 
 func TestPreemptionGC(t *testing.T) {
 	// Test that pending GC preempts running goroutines.
-	const P = 5
+	P := 5
+	N := 10
+	if testing.Short() {
+		P = 3
+		N = 2
+	}
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(P + 1))
 	var stop uint32
 	for i := 0; i < P; i++ {
@@ -224,7 +237,7 @@ func TestPreemptionGC(t *testing.T) {
 			}
 		}()
 	}
-	for i := 0; i < 10; i++ {
+	for i := 0; i < N; i++ {
 		runtime.Gosched()
 		runtime.GC()
 	}