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Commit b27ce776 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

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: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent b802ab46

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

+33 −20
Original line number Diff line number Diff line
@@ -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 },