Can any of you help us with this mess? Linux is not my strong suit. Thanks! My engineer is pulling his hair out. I would appreciate any suggestions anyone could make. -dave ross davros@raf.com ----------
From: Bruce Thompson <bt@raf.com> To: davros@fred Subject: Fw: slow network behavior with kernel 2.0.x Date: Tuesday, August 12, 1997 12:18 AM
---------- | From: Bruce Thompson <bt@raf.com> | To: linux-kernel@vger.rutgers.edu | Cc: linux-net@vger.rutgers.edu | Subject: slow network behavior with kernel 2.0.x | Date: Thursday, July 31, 1997 4:40 PM | | | My company developes a psuedo real-time client-server system that runs on | linux connected through TCP sockets. I have been noticing it has been | taking the data packets quite a while to reach the clients from the server. | After trying several different ethernet cards and speeds (TP vs thinnet,10 | vs 100), I have determined that the slow down only occures when the server | is running with a linux 2.0.x kernel (I have not tried 2.1.x). Any system | running up to 1.3.89 runs fine at full speed. I have not yet tested any | kernel between 1.3.89 and 2.0.0 | | From looking at tcpdumps, it appears that packets are not getting acked in | a timely way. I have turned off the 'delayed ack' feature of TCP and have | not seen any improvement. Here are some tcpdumps | | | Example of what I would expect to be normal. | 10:42:17.70 server > client: . 1:1461(1460) ack 98 win 31744 (DF) | 10:42:17.70 server > client: . 1461:2921(1460) ack 98 win 31744 (DF) | 10:42:17.71 client > server: . ack 2921 win 31744 (DF) | 10:42:17.71 server > client: . 2921:4381(1460) ack 98 win 31744 | 10:42:17.71 server > client: . 4381:5841(1460) ack 98 win 31744 | 10:42:17.71 server > client: . 5841:7301(1460) ack 98 win 31744 | 10:42:17.72 client > server: . ack 7301 win 31744 (DF) | 10:42:17.72 server > client: P 7301:8760(1459) ack 98 win 31744 (DF) | 10:42:17.74 client > server: . ack 8760 win 31744 (DF) | | Example of time lost with no ack of the first packet causing a 200ms delay, | and two acks that cause waits of 40ms and 70ms. | | 10:42:22.17 server > client: . 8760:10220(1460) ack 1222 win 31744 (DF) | 10:42:22.37 server > client: . 8760:10220(1460) ack 1222 win 31744 (DF) | 10:42:22.37 client > server: . ack 10220 win 31744 (DF) | 10:42:22.37 server > client: . 10220:11680(1460) ack 1222 win 31744 | 10:42:22.51 client > server: . ack 11680 win 31744 (DF) | 10:42:22.51 server > client: . 11680:13140(1460) ack 1222 win 31744 | 10:42:22.51 server > client: . 13140:14600(1460) ack 1222 win 31744 | 10:42:22.52 client > server: . ack 14600 win 31744 (DF) | 10:42:22.52 server > client: . 14600:16060(1460) ack 1222 win 31744 | 10:42:22.59 client > server: . ack 16060 win 31744 (DF) | 10:42:22.59 server > client: P 16060:17519(1459) ack 1222 win 31744 (DF) | 10:42:22.61 client > server: . ack 17519 win 31744 (DF) | | Here is a particularly bad example where the same 8760 byte file took 1.7 | seconds to be transfered. | | 10:17:14.95 server > client: . 1:1461(1460) ack 98 win 31744 (DF) | 10:17:15.14 client > server: . ack 1461 win 31744 (DF) | 10:17:15.14 server > client: . 1461:2921(1460) ack 98 win 31744 | 10:17:15.14 server > client: . 2921:4381(1460) ack 98 win 31744 | 10:17:15.44 client > server: . ack 2921 win 31744 (DF) | 10:17:15.44 server > client: . 4381:5841(1460) ack 98 win 31744 | 10:17:15.45 client > server: . ack 2921 win 31744 (DF) | 10:17:15.64 client > server: . ack 2921 win 31744 (DF) | 10:17:16.08 server > client: . 2921:4381(1460) ack 98 win 31744 | 10:17:16.27 client > server: . ack 5841 win 31744 (DF) | 10:17:16.27 server > client: . 5841:7301(1460) ack 98 win 31744 | 10:17:16.57 client > server: . ack 7301 win 31744 (DF) | 10:17:16.57 server > client: P 7301:8760(1459) ack 98 win 31744 (DF) | 10:17:16.59 client > server: . ack 8760 win 31744 (DF) | | In general, the system just seems to be slow in responding to this network | traffic. This is a private network for these systems so there should be | now problem with other traffic affecting these timings. With 1.3.x I see | total transit times on the order of 30ms on the 10Mbps network. | | The same hardware that runs slowly with 2.0.x will run quickly with only | the kernel changed. | | Any ideas as to what could be causing this? | | | Thanks, | ------------------------- | Bruce Thompson | RAF Technology | (206) 867-0700 | |