em(4) interface hangs under 8.0-RELEASE

[Nick Rogers]

I'm still having a problem where an em(4) interface mysteriously "hangs" and
mostly stops sending/receiving  packets until I issue an ifconfig emX down
followed by an ifconfig emX up, which fixes the problem for some amount of
time. Traffic on the interface is about a consistent 3mb/s.

One interesting thing to note is that if I tcpdump the interface during the
"hang", I sometimes see a portion of the expected packets, usually only
outbound.

I've tried compiling a custom 8.0-RELEASE kernel with the em(4) driver
(sys/dev/e1000) from 7.2-RELEASE as well as the same from cvs HEAD. Neither
seem to fix the problem.

I've also tried, as suggested in a previous thread, disabling TSO, TXCSUM,
RXCSUM via the following:

        sysctl net.inet.tcp.tso=0
        ifconfig em1 -tso -txcsum
        ifconfig em1 down
        ifconfig em1 up

Relevant ifconfig and pciconf dump below. There are no attached VLAN
interfaces.

em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=98<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
ether 00:04:23:ca:a7:b7
inet 172.31.1.3 netmask 0xfffffff8 broadcast 172.31.1.7
media: Ethernet autoselect (1000baseT <full-duplex>)
status: active

em1 at pci0:2:2:1: class=0x020000 card=0x11798086 chip=0x10798086 rev=0x03
hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Dual Port Gigabit Ethernet Controller (82546EB)'
    class      = network
    subclass   = ethernet
    cap 01[dc] = powerspec 2  supports D0 D3  current D0
    cap 07[e4] = PCI-X 64-bit supports 133MHz, 2048 burst read, 1 split
transaction
    cap 05[f0] = MSI supports 1 message, 64 bit

Any suggestions are greatly appreciated. Thanks.