hrtime_delta
tgt->is_crtime += hrtime_delta(path->is_crtime, path->is_snaptime);
uint64_t hrtime_delta(hrtime_t old, hrtime_t new);
t_delta = hrtime_delta(old->is_snaptime,
t_delta = hrtime_delta(new->is_crtime,
w_delta = hrtime_delta((u_longlong_t)
r_delta = hrtime_delta(old ? old->is_stats.rlentime : 0,
t_delta = hrtime_delta(old ? old->is_stats.wtime : 0,
t_delta = hrtime_delta(old ? old->is_stats.rtime : 0,