dc_tick
static void dc_tick (void *);
callout_reset(&sc->dc_stat_timer, hz / 10, dc_tick, sc);
callout_reset(&sc->dc_stat_timer, hz, dc_tick, sc);
callout_reset(&sc->dc_stat_timer, hz/10, dc_tick, sc);
callout_reset(&sc->dc_stat_timer, hz, dc_tick, sc);