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Eliminate the spinlock used when halting inactive CPU cores.

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This is a more efficient implementation.
This commit is contained in:
Martin Whitaker 2022-02-18 20:08:24 +00:00
parent f4a413cf6d
commit cadad583d7
1 changed files with 18 additions and 14 deletions
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32
app/main.c
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@ -71,8 +71,6 @@ static uintptr_t high_load_addr;
static barrier_t *start_barrier = NULL;
static spinlock_t *halt_mutex = NULL;
static volatile bool start_run = false;
static volatile bool start_pass = false;
static volatile bool start_test = false;
@ -253,7 +251,6 @@ static void global_init(void)
start_barrier = smp_alloc_barrier(1);
run_barrier = smp_alloc_barrier(1);
halt_mutex = smp_alloc_mutex();
error_mutex = smp_alloc_mutex();
start_run = true;
@ -383,15 +380,9 @@ static void test_all_windows(int my_cpu)
BARRIER;
if (!i_am_active) {
// Guard against a race between halting and being woken up.
spin_lock(halt_mutex);
if (halt_if_inactive) {
if (!dummy_run && halt_if_inactive) {
cpu_state[my_cpu] = CPU_STATE_HALTED;
spin_unlock(halt_mutex);
__asm__ __volatile__ ("hlt");
cpu_state[my_cpu] = CPU_STATE_RUNNING;
} else {
spin_unlock(halt_mutex);
}
continue;
}
@ -418,13 +409,26 @@ static void test_all_windows(int my_cpu)
if (i_am_master) {
if (!dummy_run && halt_if_inactive) {
spin_lock(halt_mutex);
halt_if_inactive = false;
spin_unlock(halt_mutex);
for (int cpu_num = 0; cpu_num < num_available_cpus; cpu_num++) {
int cpu_num = 0;
int retries = 0;
while (cpu_num < num_available_cpus) {
if (cpu_num == my_cpu) {
cpu_num++;
continue;
}
if (cpu_state[cpu_num] == CPU_STATE_ENABLED) {
// This catches a potential race between the inactive CPU halting and the master CPU waking
// it up. This should be an unlikely event, so just spin until the inactive CPU catches up.
usleep(10);
if (++retries < 1000) {
continue;
}
}
if (cpu_state[cpu_num] == CPU_STATE_HALTED) {
smp_send_nmi(cpu_num);
}
retries = 0;
cpu_num++;
}
}
window_num++;