I have a program that reads simple line feed data over tcp (XXXXXXX\r\n). In this case I am reading data from another program on the same machine. It is built on a win 2003 x64 server in vs2005. On several machines it runs fine. On others we are seeing a considerable slow down, it will only read data at about 1/10 the rate other machines will. It does not seem OS dependant (tried it on vista, xp, 2003 all with varying results) If I build it on one of the machines which sees the slowdown it will run at full speed (same source, same build configuration), and using that build on all other machines that have the problem it disappears. There is no consistency between the range of hardware and the slowdown from what I can see. Any ideas on where to look would be sooo helpful. I am going to see if wireshark can show me anything which might help tomorrow, but I have never used it before so I am not sure what I should look for.

Well after some investigation I do not think this is network related. It seems to be a bug when running on multicore cpus. (I saw it happen before years ago with everquest) using a program that sets the core affinity to 1 cpu on startup seems to fix the issue.