Just a brief update - this has been up and stable for about 32 hours - I've been periodically generating load on the system. No kernel errors of any sort so far. Actually, in retrospect, I believe the dma issue was triggering other bad things - including an rcu lockup (patched in tip - sched.c).Tracked this down. The status being returned is 0x3c0080 - good flow control packets. Nothing is actually being dropped (confirmed by packet trace on switch compared with packet trace on server).
Just as an FYI - (and this should probably be in a new thread) I am seeing an large number (>9,000,000) of dropped rx packets, however at this time I see no errors resulting from that (on this or client machines). As the # of dropped packets hasn't incremented at any time I was observing things, I can't say what this is about. Probably nothing, but I'll see if I can track down what is going on. I did see some of this earlier on while troubleshooting the sky2 issues that now seem resolved. Quick crosschecking of other machines do not show high error or retransmission rates. I'm also not seeing any evidence of other errors (no errors reported by ifconfig, or ethtool, or printk (debug is enabled).
I'm wondering whether these dropped packets are due mostly to hitting GMR_FS_RX_OK in sky2_receive. I'm also guessing that the high numbers of this that I'm seeing is an artifact of being able to pump more traffic through with the above patch. Given the description of the status code in sky2.h (receive ok) I'm wondering whether a) this should be reported as dropped, b) whether resubmit is necessary, c) whether it's possible that eth1 events coinciding with eth0 events are the cause and d) whether or not there's another issue entirely.