关于使用strace 追踪系统调用的问题

clock_gettime(CLOCK_MONOTONIC, {19709824, 440707858}) = 0
gettimeofday({1529402376, 190652}, NULL) = 0
epoll_wait(18, {{EPOLLIN, {u32=6, u64=6, 32, -1) = 1
clock_gettime(CLOCK_MONOTONIC, {19709829, 545188505}) = 0
gettimeofday({1529402381, 295127}, NULL) = 0
poll(, 1, 0) = 0 (Timeout)
epoll_wait(18
}}}