selftests/powerpc: context_switch use private futexes with threads

This reduces overhead of mutex locking and increases context switch
rate significantly (which helps to measure and profile the context
switch path).
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/benchmarks/context_switch.c

@@ -258,9 +258,14 @@ static unsigned long xchg(unsigned long *p, unsigned long val)
 	return __atomic_exchange_n(p, val, __ATOMIC_SEQ_CST);
 }
 
+static int processes;
+
 static int mutex_lock(unsigned long *m)
 {
 	int c;
+	int flags = FUTEX_WAIT;
+	if (!processes)
+		flags |= FUTEX_PRIVATE_FLAG;
 
 	c = cmpxchg(m, 0, 1);
 	if (!c)
@@ -270,7 +275,7 @@ static int mutex_lock(unsigned long *m)
 		c = xchg(m, 2);
 
 	while (c) {
-		sys_futex(m, FUTEX_WAIT, 2, NULL, NULL, 0);
+		sys_futex(m, flags, 2, NULL, NULL, 0);
 		c = xchg(m, 2);
 	}
 
@@ -279,12 +284,16 @@ static int mutex_lock(unsigned long *m)
 
 static int mutex_unlock(unsigned long *m)
 {
+	int flags = FUTEX_WAKE;
+	if (!processes)
+		flags |= FUTEX_PRIVATE_FLAG;
+
 	if (*m == 2)
 		*m = 0;
 	else if (xchg(m, 0) == 1)
 		return 0;
 
-	sys_futex(m, FUTEX_WAKE, 1, NULL, NULL, 0);
+	sys_futex(m, flags, 1, NULL, NULL, 0);
 
 	return 0;
 }
@@ -293,6 +302,11 @@ static unsigned long *m1, *m2;
 
 static void futex_setup(int cpu1, int cpu2)
 {
+	if (!processes) {
+		static unsigned long _m1, _m2;
+		m1 = &_m1;
+		m2 = &_m2;
+	} else {
 		int shmid;
 		void *shmaddr;
 
@@ -313,6 +327,7 @@ static void futex_setup(int cpu1, int cpu2)
 
 		m1 = shmaddr;
 		m2 = shmaddr + sizeof(*m1);
+	}
 
 	*m1 = 0;
 	*m2 = 0;
@@ -352,8 +367,6 @@ static struct actions futex_actions = {
 	.thread2 = futex_thread2,
 };
 
-static int processes;
-
 static struct option options[] = {
 	{ "test", required_argument, 0, 't' },
 	{ "process", no_argument, &processes, 1 },