em0 hangs without any messages like "Watchdog timeout" only down/up reset it.

[Pete French]

I havent investigated far enough yet to see if this is the same problem, but
I am also seeing hangs on em0 when under heavy load. This is 8-STABLE from
the 17 at around 3pm.

em0 at pci0:0:25:0:        class=0x020000 card=0x281e103c chip=0x10bd8086 rev=0x02 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Intel 82566DM Gigabit Ethernet Adapter (82566DM)'
    class      = network
    subclass   = ethernet

What I am doing here is using ggated/ggatec to provide drives to another
machine which is adding them into a ZFS pool. This locks up the ethernet
in about 20 minutes. Going to concole on the machine all looks fine,
but it is not possible to ping anything through the em0 interface.

I have no special tunings for em0, though I do have expanded buffer
space to improve the ggated performance

kern.ipc.maxsockbuf=1048576
net.inet.tcp.sendspace=131072
net.inet.tcp.recvspace=131072

Machine is amd64 with 6 gig of RAM.

-pete.