Intel em transmit hangs with DMA packet prefetching enabled

[Gerrit Nagelhout]

Hi,

Recently I turned on the packet prefetching feature (register TXDMAC 0x3000,
set DPP to 0).  This increases the maximum transmit performance per port by
about 50KPPS.  Everything worked fine, until one of our applications that
sends lots of data with multiple (2 - 3) mbufs per descriptor started using
this feature, and the transmitter started hanging.  The watchdog feature in
the driver catches it, and resets the chip, after which everything is good
again for a while.  Has anyone else seen this behaviour before?
Thanks,

Gerrit Nagelhout