Nehalem network performance

[Kelvin Ku]

We recently purchased our first Nehalem-based system with a single Xeon E5530
CPU. We were unable to boot FC6 on it and are trying to upgrade our network to
F11/F12 anyway, so we installed F11 on it.

Our existing hardware includes Xeon 5100- and 5400-series CPUs running mainly
FC6 (2.6.22), except for a single Xeon 5150 system running F11. Our target
application consumes multicast data during business hours and has been dropping
packets more frequently on the new hardware/OS combination than on our older
systems. I've tried using the on-board Intel 82574L dual-port NIC (e1000e
driver) and a discrete Intel 82576 dual-port NIC (igb driver). Counters for the
NIC, socket layer, and switch don't show any dropped packets.

My question is this: has anyone experienced performance degradation running a
UDP-consuming application after moving to a Nehalem-based system? We have yet
to identify whether the culprit is the hardware, the OS, or the combination of
the two. However, note that our app works fine on the 5150 system running F11
that I mentioned above.

Likewise, if you've migrated such an app to a Nehalem system and had to make
adjustments to get it to work as before, I'd like to hear from you too.

Thanks,
Kelvin Ku