mtx_delay
static struct lock_delay_config __read_frequently mtx_delay;
SYSCTL_U16(_debug_mtx, OID_AUTO, delay_base, CTLFLAG_RW, &mtx_delay.base,
SYSCTL_U16(_debug_mtx, OID_AUTO, delay_max, CTLFLAG_RW, &mtx_delay.max,
LOCK_DELAY_SYSINIT_DEFAULT(mtx_delay);
lock_delay_arg_init(&lda, &mtx_delay);