Re: [PATCH -rt DO NOT APPLY] Fix for tg3 networking lockup

On Fri, 2006-08-25 at 22:33 +0000, Marc Bevand wrote:

Still, it would be great if ASF could be disabled, because I have
noticed that when ASF is enabled, the tg3 driver automatically disables
TSO (TCP Segmentation Offloading). Here is a dmesg output from a server
where I am seeing that behavior:

  eth0: Tigon3 [partno(BCM95704A6) rev 2100 PHY(5704)] (PCIX:133MHz:64-bit) \
    10/100/1000BaseT Ethernet 00:30:48:59:c4:94
  eth0: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[1] Split[0] WireSpeed[1] TSOcap[0]
  [...]
  eth1: Tigon3 [partno(BCM95704A6) rev 2100 PHY(5704)] (PCIX:133MHz:64-bit) \
    10/100/1000BaseT Ethernet 00:30:48:59:c4:95
  eth1: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[0] Split[0] WireSpeed[1] TSOcap[1]

Both interfaces are fundamentally TSO-capable, but since ASF is enabled
on eth0, tg3 disables TSO on this interface. Of course at this point it
is not even possible to use ethtool to re-enable it because the driver
considers eth0 as not TSO-capable at all.

The reason is that TSO on 5704 and older chips is done by firmware.  ASF
is also implemented by firmware.  If ASF is enabled, there is no room to
do TSO and ASF at the same time.

Firmware-based TSO is actually slower than no TSO.  The only benefit is
a little better CPU utilization.

On the newer chips, TSO is done by hardware which solves both the ASF
and throughput problems.