![为什么我在 Linux 上通过 Wi-Fi 进行测试时会观察到周期性的延迟“峰值”?](https://linux22.com/image/1584430/%E4%B8%BA%E4%BB%80%E4%B9%88%E6%88%91%E5%9C%A8%20Linux%20%E4%B8%8A%E9%80%9A%E8%BF%87%20Wi-Fi%20%E8%BF%9B%E8%A1%8C%E6%B5%8B%E8%AF%95%E6%97%B6%E4%BC%9A%E8%A7%82%E5%AF%9F%E5%88%B0%E5%91%A8%E6%9C%9F%E6%80%A7%E7%9A%84%E5%BB%B6%E8%BF%9F%E2%80%9C%E5%B3%B0%E5%80%BC%E2%80%9D%EF%BC%9F.png)
当我尝试测量两台运行 Linux(Ubuntu 16.04 LTS)并通过公共接入点连接到 Wi-Fi(5 GHz 802.11n)的计算机之间的延迟时,我遇到了一种奇怪的行为。
在使用自定义工具(LaTe,使用 IPv4 上的 UDP - 可在此处获得)时都会发生这种情况:https://francescoraves483.github.io/LaMP_LaTe/) 以及使用 ping 时。
问题是,每隔大约 2 分钟,就会出现一些现象,导致短时间间隔内的测量速度大大减慢(延迟从 2/3 毫秒变为有时超过 200/400 毫秒),而且这种情况是周期性的。
例如,当启动一系列每次持续 1 分钟的测试时,每两次测试中就会出现一次测量缓慢的情况,同时数据包丢失率约为 5%。相反,当测试持续超过 2 分钟时,所有测试都会出现这种情况,数据包丢失率约为 2.5%,这表明可能存在一些周期性因素干扰了 ping。
您知道为什么会发生这种情况吗?在 Linux 下是否存在某些网络服务,即使用户没有明确激活它,也会在特定情况下定期激活它?
如果通过以太网 ping(或测试延迟),则不会发生相同的行为。后台也没有运行任何云服务,例如 Dropbox(在执行这些测量之前已停用 Dropbox),并且在完全不同的地方使用两台不同的计算机(在距离第一台计算机 80 多公里的房间中)通过 2.4 GHz 传输时可以观察到相同的行为。
作为附加信息,一台计算机安装了英特尔双频 Wireless-AC 8265 NIC,另一台计算机安装了高通 Atheros AR9460 NIC,后者也是双频的。
这是 LaTe 输出日志的一部分,显示了这种奇怪的行为(测试每 100 毫秒发送一个数据包):
Received a reply from 192.168.1.174 (id=64373, seq=345, rx_bytes=57). Time: 2.833 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=346, rx_bytes=57). Time: 3.717 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=347, rx_bytes=57). Time: 2.168 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=348, rx_bytes=57). Time: 2.174 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=349, rx_bytes=57). Time: 2.119 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=350, rx_bytes=57). Time: 2.118 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=351, rx_bytes=57). Time: 2.075 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=352, rx_bytes=57). Time: 2.032 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=353, rx_bytes=57). Time: 1.889 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=354, rx_bytes=57). Time: 2.010 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=355, rx_bytes=57). Time: 2.024 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=356, rx_bytes=57). Time: 2.113 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=357, rx_bytes=57). Time: 2.203 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=358, rx_bytes=57). Time: 2.014 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=359, rx_bytes=57). Time: 2.152 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=361, rx_bytes=57). Time: 147.029 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=362, rx_bytes=57). Time: 47.065 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=365, rx_bytes=57). Time: 2.150 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=366, rx_bytes=57). Time: 2.095 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=368, rx_bytes=57). Time: 61.026 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=369, rx_bytes=57). Time: 2.097 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=370, rx_bytes=57). Time: 134.886 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=372, rx_bytes=57). Time: 70.658 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=373, rx_bytes=57). Time: 1.798 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=375, rx_bytes=57). Time: 251.165 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=376, rx_bytes=57). Time: 151.179 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=378, rx_bytes=57). Time: 85.217 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=379, rx_bytes=57). Time: 1.853 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=381, rx_bytes=57). Time: 290.875 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=382, rx_bytes=57). Time: 193.427 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=384, rx_bytes=57). Time: 86.089 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=385, rx_bytes=57). Time: 1.805 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=388, rx_bytes=57). Time: 37.579 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=389, rx_bytes=57). Time: 2.214 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=390, rx_bytes=57). Time: 115.016 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=392, rx_bytes=57). Time: 235.182 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=393, rx_bytes=57). Time: 135.198 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=395, rx_bytes=57). Time: 2.143 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=396, rx_bytes=57). Time: 154.826 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=398, rx_bytes=57). Time: 54.547 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=399, rx_bytes=57). Time: 2.241 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=401, rx_bytes=57). Time: 2.111 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=402, rx_bytes=57). Time: 64.163 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=404, rx_bytes=57). Time: 69.373 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=405, rx_bytes=57). Time: 1.838 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=408, rx_bytes=57). Time: 269.563 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=409, rx_bytes=57). Time: 169.589 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=411, rx_bytes=57). Time: 1.842 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=412, rx_bytes=57). Time: 154.918 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=414, rx_bytes=57). Time: 93.432 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=415, rx_bytes=57). Time: 2.122 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=417, rx_bytes=57). Time: 2.579 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=418, rx_bytes=57). Time: 195.314 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=420, rx_bytes=57). Time: 108.841 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=421, rx_bytes=57). Time: 8.815 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=424, rx_bytes=57). Time: 308.488 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=425, rx_bytes=57). Time: 208.501 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=427, rx_bytes=57). Time: 8.505 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=428, rx_bytes=57). Time: 2.451 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=430, rx_bytes=57). Time: 4.135 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=431, rx_bytes=57). Time: 32.459 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=433, rx_bytes=57). Time: 58.180 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=434, rx_bytes=57). Time: 2.145 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=436, rx_bytes=57). Time: 20.896 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=437, rx_bytes=57). Time: 2.144 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=440, rx_bytes=57). Time: 30.552 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=441, rx_bytes=57). Time: 2.237 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=442, rx_bytes=57). Time: 115.026 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=444, rx_bytes=57). Time: 40.270 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=445, rx_bytes=57). Time: 2.037 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=447, rx_bytes=57). Time: 255.116 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=448, rx_bytes=57). Time: 155.147 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=450, rx_bytes=57). Time: 54.869 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=451, rx_bytes=57). Time: 2.349 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=453, rx_bytes=57). Time: 53.936 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=454, rx_bytes=57). Time: 2.153 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=455, rx_bytes=57). Time: 2.159 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=456, rx_bytes=57). Time: 2.106 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=457, rx_bytes=57). Time: 2.019 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=458, rx_bytes=57). Time: 2.107 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=459, rx_bytes=57). Time: 2.159 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=460, rx_bytes=57). Time: 2.170 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=461, rx_bytes=57). Time: 2.156 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=462, rx_bytes=57). Time: 2.155 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=463, rx_bytes=57). Time: 2.165 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=464, rx_bytes=57). Time: 2.192 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=465, rx_bytes=57). Time: 2.031 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=466, rx_bytes=57). Time: 2.094 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=467, rx_bytes=57). Time: 2.098 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=468, rx_bytes=57). Time: 2.076 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=469, rx_bytes=57). Time: 2.110 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=470, rx_bytes=57). Time: 2.109 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=471, rx_bytes=57). Time: 2.168 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=472, rx_bytes=57). Time: 3.457 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=473, rx_bytes=57). Time: 4.354 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=474, rx_bytes=57). Time: 2.142 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=475, rx_bytes=57). Time: 2.140 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=476, rx_bytes=57). Time: 2.156 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=477, rx_bytes=57). Time: 2.150 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=478, rx_bytes=57). Time: 2.157 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=479, rx_bytes=57). Time: 2.097 ms (User-to-user)
Received a reply from 192.168.1.174 (id=64373, seq=480, rx_bytes=57). Time: 2.173 ms (User-to-user)
提前非常感谢您。