The e1000 and e1000e drivers for Intel PRO/1000 network devices were updated with an enhanced algorithm for adaptive interrupt modulation in the Red Hat Enterprise Linux 5.1 release. When InterruptThrottleRate was set to "1" (thus enabling the new adaptive mode), certain traffic patterns could have caused high CPU usage. This update provides a way to set InterruptThrottleRate to "4", which switches the mode back to the simpler and non-adaptive algorithm. Doing so may decrease CPU usage by the e1000 and e1000e drivers depending on traffic patterns.
Note: you can change the InterruptThrottleRate setting using the ethtool utility by running the following command:
ethtool -C ethX rx-usecs 4