I've read through other threads on performance differences between RHEL6 and RHEL5, but none seem a tight match to mine.

My issue manifests itself in slightly slower average response time (20ms) per request. I have about 10/10 servers of the same hardware spec with Cent6.1 and Cent5.6. The issue is consistent across the group.

I am running Ruby on Rails with Passenger.

• Apache config is identical (checked out from the same SVN repo)
• Ruby and Passenger are identical builds.
• Application is identical and being served traffic round robin.
• mod_worker

An interesting clue from server-status: The Cent6.1 servers have a steady 20-40 threads in the "Reading Request" state while the Cent5.6 servers have around 1. I'm graphing this so I can see it trend over time.

I also have a bunch of much newer machines that are significantly faster and are running Cent6.1. They dust all the older machines in response time, but I can see they also have a steady 20-40 threads in the "Reading Request" state. This makes me believe I can get their response time down, if I can figure out what is holding up these requests.

My gut is telling me that I need to tune some network setting in sysctl, but I haven't figured it out yet. Help is appreciated.