ix0 and ix1 ifconfig options different on Supermicro board

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I have nearly identical setups, but ix0 and ix1 are getting different 
options at boot.  This seems to be the only difference I see between 
machines and I am trying to answer the question, Why can Server A iperf 
close to line rate while the other servers can not?

The Test:  iperf -P 3 -c REMOTE_ADDR

Server A (ix1) -> Server C (ix0)  = 9.4Gbps
Server B (ix0)-> Server C (ix0) = 5.6Gbps
Server C (ix0)-> A (ix1) or B (ix0)  = 5.0Gbps


The motherboards are identical between A,B and C and the configs very 
similar.  The only difference is that Server A is plugged into ix1 while 
Server B and C are using ix0.


I am not modifying the flags at boot (eg ifconfig -tso), yet ix0 lacks 
TXCSUM,TSO4,TSO6,LRO,WOL.

ix0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 
mtu 1500
options=a538b9<RXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6>
         ether *ac:1f:6b:6a:14:6*4
         media: Ethernet autoselect (10Gbase-T <full-duplex>)
ix1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=e53fbb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,LRO,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
         ether *ac:1f:6b:6a:14:6*5
         media: Ethernet autoselect (10Gbase-T <full-duplex>)

I did try adding some flags to ix0 and -- not sure if this was the 
reason -- the box started acting oddly and I ended up rebooting it.


My hunch has is that there is somethign with the TSO4.


Rudy