sk_tick
static void sk_tick(void *);
callout_reset(&sc_if->sk_tick_ch, hz, sk_tick, sc_if);
callout_reset(&sc_if->sk_tick_ch, hz, sk_tick, sc_if);
callout_reset(&sc_if->sk_tick_ch, hz, sk_tick, sc_if);
callout_reset(&sc_if->sk_tick_ch, hz, sk_tick, sc_if);