[問答] 關於 gigabit 網路卡

[gn00618777 (非常念舊)]

事情是這樣的

我這邊有一個 freescale 的開發板。要用 iperf 指令來測試他的 throughput

板子和筆電之間對連，兩邊都有安裝 iperf。


我筆電當 server:  iperf.exe -s -w 256K -i 1 -M 64
  板子當 client:  iperf -c 10.10.10.1 -i 1 -w 256K -M 64

       MTU 為 64

       結果:  效能接近官方文件的 400Mbps

              [  3]  0.0- 1.0 sec  41.8 MBytes   350 Mbits/sec

                [  3]  1.0- 2.0 sec  38.5 MBytes   323 Mbits/sec

                [  3]  2.0- 3.0 sec  42.4 MBytes   355 Mbits/sec

                [  3]  3.0- 4.0 sec  49.0 MBytes   411 Mbits/sec

                [  3]  4.0- 5.0 sec  49.4 MBytes   414 Mbits/sec

                [  3]  5.0- 6.0 sec  50.2 MBytes   422 Mbits/sec

                [  3]  6.0- 7.0 sec  50.4 MBytes   423 Mbits/sec

                [  3]  7.0- 8.0 sec  44.1 MBytes   370 Mbits/sec

                [  3]  8.0- 9.0 sec  44.5 MBytes   373 Mbits/sec

                [  3]  9.0-10.0 sec  47.1 MBytes   395 Mbits/sec

                [  3]  0.0-10.0 sec   458 MBytes   384 Mbits/sec


===========================================================================

      如果我改為

                  iperf.exe -s -w 256K -i 1 -M 128   (筆電)
                   iperf -c 10.10.10.1 -i 1 -w 256K -M 128 (板子)

         效能其差無比:

                     [  3]  0.0- 1.0 sec  5.88 MBytes  49.3 Mbits/sec

        [  3]  1.0- 2.0 sec  6.38 MBytes  53.5 Mbits/sec

        [  3]  2.0- 3.0 sec  6.25 MBytes  52.4 Mbits/sec

        [  3]  3.0- 4.0 sec  6.38 MBytes  53.5 Mbits/sec

        [  3]  4.0- 5.0 sec  6.25 MBytes  52.4 Mbits/sec

        [  3]  5.0- 6.0 sec  6.25 MBytes 52.4 Mbits/sec

       [  3]  6.0- 7.0 sec  6.38 MBytes  53.5 Mbits/sec

       [  3]  7.0- 8.0 sec  6.25 MBytes  52.4 Mbits/sec

       [  3]  8.0- 9.0 sec  6.25 MBytes  52.4 Mbits/sec

       [  3]  9.0-10.0 sec  6.25 MBytes  52.4 Mbits/sec

       [  3]  0.0-10.0 sec  62.6 MBytes  52.5 Mbits/sec

=============================================================================

     如果我將 MTU 改成 -M 256 512 1024 1280 1518 ，會慢慢趨近於400，且從 -M 128
     開始，throughput 大約是兩倍增加，也就是上面的數值x2，這樣似乎 MTU 成了
     關鍵，有沒有高手能夠為我解惑這種行為?


     我單獨用筆電做測試 ping wwww.google.com -f -l xxxx

 去算他的 MTU，發現用 128 也是會卡卡的，最後xxxx數值為 1468 才比較順，總而言之

 上面筆電和板子對連結果，我不知道為何從 -M 64 變成 -128 效能會差那麼多.....


懇請指教，謝謝。

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