Does Linux 2.6 support zero-copy on the RX side?

Does the Linux TCP/IP stack support zero-copy (along with checksum offload)
on the RX side? We've been developing an Ethernet controller and driver
that supports checksum offload and see good improvements in throughput on
the TX side (e.g., 100%), but only marginal improvement on the RX side
(e.g., 20%). Right now we're using Linux 2.4.20. We think the lack of
improvement on the RX side is because of the buffer copy from kernel space
to user space of the received data. We're using netperf/netserver to get
performance measurements, so we're using the TCP_SENDFILE option for the TX
side. Any thoughts?

Thanks,
-Rick