pf_purge_thread
tsleep(pf_purge_thread, PWAIT, "pftm", 1 * hz);
wakeup(pf_purge_thread);
wakeup(pf_purge_thread);
if (kthread_create(pf_purge_thread, NULL, NULL, "pfpurge"))
wakeup_one(pf_purge_thread);
tsleep(pf_purge_thread, 0, "pftmo", hz / 10);
extern void pf_purge_thread(void *);