Fw: slow network behavior with Linux kernel 2.0.x

["Dave Ross" <davros@raf.com>]

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
> | 
> |