xnu-4903.270.47.tar.gz

[apple/xnu.git] / osfmk / kern / test_lock.c

#include <mach_ldebug.h>
#include <debug.h>

#include <mach/kern_return.h>
#include <mach/mach_host_server.h>
#include <mach_debug/lockgroup_info.h>

#include <kern/locks.h>
#include <kern/misc_protos.h>
#include <kern/kalloc.h>
#include <kern/thread.h>
#include <kern/processor.h>
#include <kern/sched_prim.h>
#include <kern/debug.h>
#include <libkern/section_keywords.h>
#include <machine/atomic.h>
#include <machine/machine_cpu.h>
#include <machine/atomic.h>
#include <string.h>
#include <kern/kalloc.h>

#include <sys/kdebug.h>

static lck_mtx_t        test_mtx;
static lck_grp_t        test_mtx_grp;
static lck_grp_attr_t   test_mtx_grp_attr;
static lck_attr_t       test_mtx_attr;

static lck_grp_t        test_mtx_stats_grp;
static lck_grp_attr_t   test_mtx_stats_grp_attr;
static lck_attr_t       test_mtx_stats_attr;

struct lck_mtx_test_stats_elem {
        lck_spin_t      lock;
        uint64_t        samples;
        uint64_t        avg;
        uint64_t        max;
        uint64_t        min;
        uint64_t        tot;
};

#define TEST_MTX_LOCK_STATS                     0
#define TEST_MTX_TRY_LOCK_STATS                 1
#define TEST_MTX_LOCK_SPIN_STATS                2
#define TEST_MTX_LOCK_SPIN_ALWAYS_STATS         3
#define TEST_MTX_TRY_LOCK_SPIN_STATS            4
#define TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS     5
#define TEST_MTX_UNLOCK_MTX_STATS               6
#define TEST_MTX_UNLOCK_SPIN_STATS              7
#define TEST_MTX_MAX_STATS                      8

struct lck_mtx_test_stats_elem lck_mtx_test_stats[TEST_MTX_MAX_STATS];
atomic_bool enabled = TRUE;

static void
init_test_mtx_stats(void)
{
        int i;

        lck_grp_attr_setdefault(&test_mtx_stats_grp_attr);
        lck_grp_init(&test_mtx_stats_grp, "testlck_stats_mtx", &test_mtx_stats_grp_attr);
        lck_attr_setdefault(&test_mtx_stats_attr);

        atomic_store(&enabled, TRUE);
        for (i = 0; i < TEST_MTX_MAX_STATS; i++) {
                memset(&lck_mtx_test_stats[i], 0, sizeof(struct lck_mtx_test_stats_elem));
                lck_mtx_test_stats[i].min = ~0;
                lck_spin_init(&lck_mtx_test_stats[i].lock, &test_mtx_stats_grp, &test_mtx_stats_attr);
        }
}

static void
update_test_mtx_stats(
        uint64_t start,
        uint64_t end,
        uint type)
{
        if (atomic_load(&enabled) == TRUE) {
                assert(type < TEST_MTX_MAX_STATS);
                assert(start <= end);

                uint64_t elapsed = end - start;
                struct lck_mtx_test_stats_elem* stat = &lck_mtx_test_stats[type];

                lck_spin_lock(&stat->lock);

                stat->samples++;
                stat->tot += elapsed;
                stat->avg = stat->tot / stat->samples;
                if (stat->max < elapsed) {
                        stat->max = elapsed;
                }
                if (stat->min > elapsed) {
                        stat->min = elapsed;
                }
                lck_spin_unlock(&stat->lock);
        }
}

static void
erase_test_mtx_stats(
        uint type)
{
        assert(type < TEST_MTX_MAX_STATS);
        struct lck_mtx_test_stats_elem* stat = &lck_mtx_test_stats[type];

        lck_spin_lock(&stat->lock);

        stat->samples = 0;
        stat->tot = 0;
        stat->avg = 0;
        stat->max = 0;
        stat->min = ~0;

        lck_spin_unlock(&stat->lock);
}

void
erase_all_test_mtx_stats(void)
{
        int i;
        for (i = 0; i < TEST_MTX_MAX_STATS; i++) {
                erase_test_mtx_stats(i);
        }
}

static void
disable_all_test_mtx_stats(void)
{
        atomic_store(&enabled, FALSE);
}

static void
enable_all_test_mtx_stats(void)
{
        atomic_store(&enabled, TRUE);
}

static int
print_test_mtx_stats_string_name(
        int type_num,
        char* buffer,
        int size)
{
        char* type = "";
        switch (type_num) {
        case TEST_MTX_LOCK_STATS:
                type = "TEST_MTX_LOCK_STATS";
                break;
        case TEST_MTX_TRY_LOCK_STATS:
                type = "TEST_MTX_TRY_LOCK_STATS";
                break;
        case TEST_MTX_LOCK_SPIN_STATS:
                type = "TEST_MTX_LOCK_SPIN_STATS";
                break;
        case TEST_MTX_LOCK_SPIN_ALWAYS_STATS:
                type = "TEST_MTX_LOCK_SPIN_ALWAYS_STATS";
                break;
        case TEST_MTX_TRY_LOCK_SPIN_STATS:
                type = "TEST_MTX_TRY_LOCK_SPIN_STATS";
                break;
        case TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS:
                type = "TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS";
                break;
        case TEST_MTX_UNLOCK_MTX_STATS:
                type = "TEST_MTX_UNLOCK_MTX_STATS";
                break;
        case TEST_MTX_UNLOCK_SPIN_STATS:
                type = "TEST_MTX_UNLOCK_SPIN_STATS";
                break;
        default:
                break;
        }

        return snprintf(buffer, size, "%s ", type);
}

int
get_test_mtx_stats_string(
        char* buffer,
        int size)
{
        int string_off = 0;
        int ret = 0;

        ret = snprintf(&buffer[string_off], size, "\n");
        size -= ret;
        string_off += ret;

        int i;
        for (i = 0; i < TEST_MTX_MAX_STATS; i++) {
                struct lck_mtx_test_stats_elem* stat = &lck_mtx_test_stats[i];

                ret = snprintf(&buffer[string_off], size, "{ ");
                size -= ret;
                string_off += ret;

                lck_spin_lock(&stat->lock);
                uint64_t time;

                ret = snprintf(&buffer[string_off], size, "samples %llu, ", stat->samples);
                size -= ret;
                string_off += ret;

                absolutetime_to_nanoseconds(stat->tot, &time);
                ret = snprintf(&buffer[string_off], size, "tot %llu ns, ", time);
                size -= ret;
                string_off += ret;

                absolutetime_to_nanoseconds(stat->avg, &time);
                ret = snprintf(&buffer[string_off], size, "avg %llu ns, ", time);
                size -= ret;
                string_off += ret;

                absolutetime_to_nanoseconds(stat->max, &time);
                ret = snprintf(&buffer[string_off], size, "max %llu ns, ", time);
                size -= ret;
                string_off += ret;

                absolutetime_to_nanoseconds(stat->min, &time);
                ret = snprintf(&buffer[string_off], size, "min %llu ns", time);
                size -= ret;
                string_off += ret;

                lck_spin_unlock(&stat->lock);

                ret = snprintf(&buffer[string_off], size, " } ");
                size -= ret;
                string_off += ret;

                ret = print_test_mtx_stats_string_name(i, &buffer[string_off], size);
                size -= ret;
                string_off += ret;

                ret = snprintf(&buffer[string_off], size, "\n");
                size -= ret;
                string_off += ret;
        }

        return string_off;
}

void
lck_mtx_test_init(void)
{
        static int first = 0;

        /*
         * This should be substituted with a version
         * of dispatch_once for kernel (rdar:39537874)
         */
        if (os_atomic_load(&first, acquire) >= 2) {
                return;
        }

        if (os_atomic_cmpxchg(&first, 0, 1, relaxed)) {
                lck_grp_attr_setdefault(&test_mtx_grp_attr);
                lck_grp_init(&test_mtx_grp, "testlck_mtx", &test_mtx_grp_attr);
                lck_attr_setdefault(&test_mtx_attr);
                lck_mtx_init(&test_mtx, &test_mtx_grp, &test_mtx_attr);

                init_test_mtx_stats();

                os_atomic_inc(&first, release);
        }

        while (os_atomic_load(&first, acquire) < 2) {
                ;
        }
}

void
lck_mtx_test_lock(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_lock(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_LOCK_STATS);
}

static void
lck_mtx_test_try_lock(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_try_lock(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_TRY_LOCK_STATS);
}

static void
lck_mtx_test_lock_spin(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_lock_spin(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_LOCK_SPIN_STATS);
}

static void
lck_mtx_test_lock_spin_always(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_lock_spin_always(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_LOCK_SPIN_ALWAYS_STATS);
}

static void
lck_mtx_test_try_lock_spin(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_try_lock_spin(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_TRY_LOCK_SPIN_STATS);
}

static void
lck_mtx_test_try_lock_spin_always(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_try_lock_spin_always(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS);
}

void
lck_mtx_test_unlock(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_unlock(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_UNLOCK_MTX_STATS);
}

static void
lck_mtx_test_unlock_mtx(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_unlock(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_UNLOCK_MTX_STATS);
}

static void
lck_mtx_test_unlock_spin(void)
{
        uint64_t start;

        start = mach_absolute_time();

        lck_mtx_unlock(&test_mtx);

        update_test_mtx_stats(start, mach_absolute_time(), TEST_MTX_UNLOCK_SPIN_STATS);
}

#define WARMUP_ITER     1000

int
lck_mtx_test_mtx_uncontended_loop_time(
        int iter, char *buffer, int size)
{
        int i;
        uint64_t tot_time[TEST_MTX_MAX_STATS];
        uint64_t run_time[TEST_MTX_MAX_STATS];
        uint64_t start;
        uint64_t start_run;

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_lock(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_lock(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_LOCK_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_LOCK_STATS]);

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_try_lock(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_try_lock(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_TRY_LOCK_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_TRY_LOCK_STATS]);

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_lock_spin(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_lock_spin(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_LOCK_SPIN_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_LOCK_SPIN_STATS]);

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_lock_spin_always(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_lock_spin_always(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_LOCK_SPIN_ALWAYS_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_LOCK_SPIN_ALWAYS_STATS]);

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_try_lock_spin(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_try_lock_spin(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_TRY_LOCK_SPIN_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_TRY_LOCK_SPIN_STATS]);

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_try_lock_spin_always(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        start_run = thread_get_runtime_self();
        start = mach_absolute_time();

        for (i = 0; i < iter; i++) {
                lck_mtx_try_lock_spin_always(&test_mtx);
                lck_mtx_unlock(&test_mtx);
        }

        absolutetime_to_nanoseconds(mach_absolute_time() - start, &tot_time[TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS]);
        absolutetime_to_nanoseconds(thread_get_runtime_self() - start_run, &run_time[TEST_MTX_TRY_LOCK_SPIN_ALWAYS_STATS]);

        int string_off = 0;
        int ret = 0;

        ret = snprintf(&buffer[string_off], size, "\n");
        size -= ret;
        string_off += ret;

        for (i = 0; i < TEST_MTX_MAX_STATS - 2; i++) {
                ret = snprintf(&buffer[string_off], size, "total time %llu ns total run time %llu ns ", tot_time[i], run_time[i]);
                size -= ret;
                string_off += ret;

                ret = print_test_mtx_stats_string_name(i, &buffer[string_off], size);
                size -= ret;
                string_off += ret;

                ret = snprintf(&buffer[string_off], size, "\n");
                size -= ret;
                string_off += ret;
        }

        return string_off;
}

static kern_return_t
lck_mtx_test_mtx_lock_uncontended(
        int iter)
{
        int i;

        disable_all_test_mtx_stats();

        //warming up the test for lock
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_lock();
                lck_mtx_test_unlock_mtx();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_lock();
                lck_mtx_test_unlock_mtx();
        }

        disable_all_test_mtx_stats();

        //warming up the test for try_lock
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_try_lock();
                lck_mtx_test_unlock_mtx();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_try_lock();
                lck_mtx_test_unlock_mtx();
        }

        return KERN_SUCCESS;
}

static kern_return_t
lck_mtx_test_mtx_spin_uncontended(
        int iter)
{
        int i;

        disable_all_test_mtx_stats();

        //warming up the test for lock_spin
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_lock_spin();
                lck_mtx_test_unlock_spin();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_lock_spin();
                lck_mtx_test_unlock_spin();
        }

        disable_all_test_mtx_stats();

        //warming up the test for try_lock_spin
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_try_lock_spin();
                lck_mtx_test_unlock_spin();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_try_lock_spin();
                lck_mtx_test_unlock_spin();
        }

        disable_all_test_mtx_stats();

        //warming up the test for lock_spin_always
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_lock_spin_always();
                lck_mtx_test_unlock_spin();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_lock_spin_always();
                lck_mtx_test_unlock_spin();
        }

        disable_all_test_mtx_stats();

        //warming up the test for try_lock_spin_always
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_try_lock_spin_always();
                lck_mtx_test_unlock_spin();
        }

        enable_all_test_mtx_stats();

        for (i = 0; i < iter; i++) {
                lck_mtx_test_try_lock_spin_always();
                lck_mtx_test_unlock_spin();
        }

        return KERN_SUCCESS;
}

int
lck_mtx_test_mtx_uncontended(
        int iter,
        char *buffer,
        int size)
{
        erase_all_test_mtx_stats();
        lck_mtx_test_mtx_lock_uncontended(iter);
        lck_mtx_test_mtx_spin_uncontended(iter);

        return get_test_mtx_stats_string(buffer, size);
}

static int synch;
static int wait_barrier;
static int iterations;
static uint64_t start_loop_time;
static uint64_t start_loop_time_run;
static uint64_t end_loop_time;
static uint64_t end_loop_time_run;

struct lck_mtx_thread_arg {
        int my_locked;
        int* other_locked;
        thread_t other_thread;
};

static void
test_mtx_lock_unlock_contended_thread(
        void *arg,
        __unused wait_result_t wr)
{
        int i, val;
        struct lck_mtx_thread_arg *info = (struct lck_mtx_thread_arg *) arg;
        thread_t other_thread;
        int* my_locked;
        int* other_locked;

        printf("Starting thread %p\n", current_thread());

        while (os_atomic_load(&info->other_thread, acquire) == NULL) {
                ;
        }
        other_thread = info->other_thread;

        printf("Other thread %p\n", other_thread);

        my_locked = &info->my_locked;
        other_locked = info->other_locked;

        *my_locked = 0;
        val = os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 2) {
                ;
        }

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_test_lock();

                os_atomic_xchg(my_locked, 1, relaxed);
                if (i != WARMUP_ITER - 1) {
                        while (os_atomic_load(&other_thread->state, relaxed) & TH_RUN) {
                                ;
                        }
                        os_atomic_xchg(my_locked, 0, relaxed);
                }

                lck_mtx_test_unlock();

                if (i != WARMUP_ITER - 1) {
                        while (os_atomic_load(other_locked, relaxed) == 0) {
                                ;
                        }
                }
        }

        printf("warmup done %p\n", current_thread());
        os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 4) {
                ;
        }

        //erase statistics
        if (val == 1) {
                erase_all_test_mtx_stats();
        }

        *my_locked = 0;
        /*
         * synch the threads so they start
         * concurrently.
         */
        os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 6) {
                ;
        }

        for (i = 0; i < iterations; i++) {
                lck_mtx_test_lock();

                os_atomic_xchg(my_locked, 1, relaxed);
                if (i != iterations - 1) {
                        while (os_atomic_load(&other_thread->state, relaxed) & TH_RUN) {
                                ;
                        }
                        os_atomic_xchg(my_locked, 0, relaxed);
                }
                lck_mtx_test_unlock_mtx();

                if (i != iterations - 1) {
                        while (os_atomic_load(other_locked, relaxed) == 0) {
                                ;
                        }
                }
        }

        os_atomic_inc(&wait_barrier, relaxed);
        thread_wakeup((event_t) &wait_barrier);
        thread_terminate_self();
}


kern_return_t
lck_mtx_test_mtx_contended(
        int iter,
        char* buffer,
        int buffer_size)
{
        thread_t thread1, thread2;
        kern_return_t result;
        struct lck_mtx_thread_arg targs[2] = {};
        synch = 0;
        wait_barrier = 0;
        iterations = iter;

        erase_all_test_mtx_stats();

        targs[0].other_thread = NULL;
        targs[1].other_thread = NULL;

        result = kernel_thread_start((thread_continue_t)test_mtx_lock_unlock_contended_thread, &targs[0], &thread1);
        if (result != KERN_SUCCESS) {
                return 0;
        }

        result = kernel_thread_start((thread_continue_t)test_mtx_lock_unlock_contended_thread, &targs[1], &thread2);
        if (result != KERN_SUCCESS) {
                thread_deallocate(thread1);
                return 0;
        }

        /* this are t1 args */
        targs[0].my_locked = 0;
        targs[0].other_locked = &targs[1].my_locked;

        os_atomic_xchg(&targs[0].other_thread, thread2, release);

        /* this are t2 args */
        targs[1].my_locked = 0;
        targs[1].other_locked = &targs[0].my_locked;

        os_atomic_xchg(&targs[1].other_thread, thread1, release);

        while (os_atomic_load(&wait_barrier, relaxed) != 2) {
                assert_wait((event_t) &wait_barrier, THREAD_UNINT);
                if (os_atomic_load(&wait_barrier, relaxed) != 2) {
                        (void) thread_block(THREAD_CONTINUE_NULL);
                } else {
                        clear_wait(current_thread(), THREAD_AWAKENED);
                }
        }

        thread_deallocate(thread1);
        thread_deallocate(thread2);

        return get_test_mtx_stats_string(buffer, buffer_size);
}

static void
test_mtx_lck_unlock_contended_loop_time_thread(
        __unused void *arg,
        __unused wait_result_t wr)
{
        int i, val;
        struct lck_mtx_thread_arg *info = (struct lck_mtx_thread_arg *) arg;
        thread_t other_thread;
        int* my_locked;
        int* other_locked;

        printf("Starting thread %p\n", current_thread());

        while (os_atomic_load(&info->other_thread, acquire) == NULL) {
                ;
        }
        other_thread = info->other_thread;

        printf("Other thread %p\n", other_thread);

        my_locked = &info->my_locked;
        other_locked = info->other_locked;

        *my_locked = 0;
        val = os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 2) {
                ;
        }

        //warming up the test
        for (i = 0; i < WARMUP_ITER; i++) {
                lck_mtx_lock(&test_mtx);

                os_atomic_xchg(my_locked, 1, relaxed);
                if (i != WARMUP_ITER - 1) {
                        while (os_atomic_load(&other_thread->state, relaxed) & TH_RUN) {
                                ;
                        }
                        os_atomic_xchg(my_locked, 0, relaxed);
                }

                lck_mtx_unlock(&test_mtx);

                if (i != WARMUP_ITER - 1) {
                        while (os_atomic_load(other_locked, relaxed) == 0) {
                                ;
                        }
                }
        }

        printf("warmup done %p\n", current_thread());

        os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 4) {
                ;
        }

        *my_locked = 0;

        /*
         * synch the threads so they start
         * concurrently.
         */
        os_atomic_inc(&synch, relaxed);
        while (os_atomic_load(&synch, relaxed) < 6) {
                ;
        }

        if (val == 1) {
                start_loop_time_run = thread_get_runtime_self();
                start_loop_time = mach_absolute_time();
        }

        for (i = 0; i < iterations; i++) {
                lck_mtx_lock(&test_mtx);

                os_atomic_xchg(my_locked, 1, relaxed);
                if (i != iterations - 1) {
                        while (os_atomic_load(&other_thread->state, relaxed) & TH_RUN) {
                                ;
                        }
                        os_atomic_xchg(my_locked, 0, relaxed);
                }

                lck_mtx_unlock(&test_mtx);

                if (i != iterations - 1) {
                        while (os_atomic_load(other_locked, relaxed) == 0) {
                                ;
                        }
                }
        }

        if (val == 1) {
                end_loop_time = mach_absolute_time();
                end_loop_time_run = thread_get_runtime_self();
        }

        os_atomic_inc(&wait_barrier, relaxed);
        thread_wakeup((event_t) &wait_barrier);
        thread_terminate_self();
}


int
lck_mtx_test_mtx_contended_loop_time(
        int iter,
        char *buffer,
        int buffer_size)
{
        thread_t thread1, thread2;
        kern_return_t result;
        int ret;
        struct lck_mtx_thread_arg targs[2] = {};
        synch = 0;
        wait_barrier = 0;
        iterations = iter;
        uint64_t time, time_run;

        targs[0].other_thread = NULL;
        targs[1].other_thread = NULL;

        result = kernel_thread_start((thread_continue_t)test_mtx_lck_unlock_contended_loop_time_thread, &targs[0], &thread1);
        if (result != KERN_SUCCESS) {
                return 0;
        }

        result = kernel_thread_start((thread_continue_t)test_mtx_lck_unlock_contended_loop_time_thread, &targs[1], &thread2);
        if (result != KERN_SUCCESS) {
                thread_deallocate(thread1);
                return 0;
        }

        /* this are t1 args */
        targs[0].my_locked = 0;
        targs[0].other_locked = &targs[1].my_locked;

        os_atomic_xchg(&targs[0].other_thread, thread2, release);

        /* this are t2 args */
        targs[1].my_locked = 0;
        targs[1].other_locked = &targs[0].my_locked;

        os_atomic_xchg(&targs[1].other_thread, thread1, release);

        while (os_atomic_load(&wait_barrier, acquire) != 2) {
                assert_wait((event_t) &wait_barrier, THREAD_UNINT);
                if (os_atomic_load(&wait_barrier, acquire) != 2) {
                        (void) thread_block(THREAD_CONTINUE_NULL);
                } else {
                        clear_wait(current_thread(), THREAD_AWAKENED);
                }
        }

        thread_deallocate(thread1);
        thread_deallocate(thread2);

        absolutetime_to_nanoseconds(end_loop_time - start_loop_time, &time);
        absolutetime_to_nanoseconds(end_loop_time_run - start_loop_time_run, &time_run);

        ret = snprintf(buffer, buffer_size, "\n");
        ret += snprintf(&buffer[ret], buffer_size - ret, "total time %llu ns total run time %llu ns ", time, time_run);
        ret += print_test_mtx_stats_string_name(TEST_MTX_LOCK_STATS, &buffer[ret], buffer_size - ret);
        ret += snprintf(&buffer[ret], buffer_size - ret, "\n");

        return ret;
}