lighttpd+dispatch.fcgi *very* slow, even before app gets control


We are running Rails + lighttpd + fastcgi (dispatch.fcgi).

At a customer site, we are seeing very slow responses. I have turned on Rails debug logs to see where the bottleneck is.

From watching the system, I can see that dispatch.fcgi runs for about 10 seconds before any logs are written. The process runs at about 100% cpu for this time.

How can I track down this problem? Has anyone seen anything like this before?