ppc + netfilter rx performance issues

Hi Folks,

Hope to humbly ask for some advice if this list is still active.  I’m supporting a legacy product and looking to improve networking performance.  It is a PPC460GT used as a bridge device with an ethernet 1Gb (marvell), that routes packets to a pci network card (using igb).
Going in the pci interface and out tx to the network, we get a nominal 700Mb, however…

RX - to the marvell we see two things:
1. 300Mbps
2. sys = 100%

Any ideas?  I’m suspicious that packets are not being handled at a low level and getting copied through iptables rules to userspace.  Maybe there is a way to enable DMA to the benefit of incoming packets?

Linux mbu-100 2.6.33.1 #245 Fri Nov 1 17:41:21 PDT 2013 ppc GNU/Linux
Glacier 

Thanks!
Bill