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。