netmap & chelsio

[np at freebsd.org]

On Thu, Jul 05, 2018 at 03:09:33PM +0000, Eggert, Lars wrote:
> Hi,
> 
> when receiving packets via netmap (current GitHub version) on a Chelsio T6
> vcc0 device on -CURRENT, it appears that the Ethernet header starts at an
> offset of two bytes into the netmap slot. So far, I have only used netmap with
> various Intel NICs, where the Ethernet header starts at offset zero.
> 
> Is this a bug? Is this to be expected?

Set hw.cxgbe.fl_pktshift=0 in loader.conf to stop the chip from doing
this.  See cxgbe(4) for details on the knob.  It's a historic
optimization that doesn't seem to matter on modern CPUs, so the driver
default should probably be 0 instead of 2.

Regards,
Navdeep