network connection

[halesnil]

There is message in log:

[notice] conn_close_if_marked(): Something wrong with your network 
connection? We tried to write () bytes to addr [scrubbed] (fd 12, type 
OR, state 5) but timed out. (Marked at main.c:715)

Several like entries every day. Sites loaded normal speed when tor first 
started, loaded very slowly after entries. Didn't touch router or 
anything. How to find out what's wrong with connection?

Thank you for help.