netmap ixgbevf mtu

[Vincenzo Maffione]

First, please make sure to use the latest netmap from github.

Yes, drivers in general use 2K or 4K RX buffers regardless of the MTU or
netmap buffer size.
To receive a frame larger than the RX buffer size you need multiple netmap
slots (as multiple descriptors are
used by the hardware), looking at the NS_MOREFRAG flag.
See the example code in utils/functional.c::rx_one().
Also TX may have per-slot limitations (e.g. due to the size of the NIC TX
fifo), but this is usually > 9K, so using a single descriptor per packet
should always
be ok. However, you can also use multiple slots on the TX side (see
utils/functional.c::tx_one()).

You need to set the buf_size parameter to the RX buffer size.
Currently we miss a mechanism for netmap to get the actual RX buffer size
from the NIC driver, so we assume 4K.
We need to check that buf_size is >= RX buffer size. This mechanism will be
added soon.

Cheers,
  Vincenzo

2018-03-16 23:52 GMT+01:00 Joe Buehler <aspam at cox.net>:

> Sorry, I should have added, this is LINUX if it matters.
>
> Joe Buehler wrote:
> > I am having difficulties with netmap over top of ixgbevf when attempting
> to use a large MTU (say 9000 bytes).
> >
> > Does the ixgbevf driver use 2048 byte buffers for RX regardless of the
> MTU or netmap buffer size?
> >
> > I can send large frames just fine but inbound frames are passed via
> netmap as 2048 bytes max.  It is possible that netmap is passing frames in
> multiple pieces I suppose, I haven't checked that yet -- my code is looking
> at the frame headers only at the moment so would toss trailing pieces.
> >
> > Joe Buehler
> >
> >
>
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-- 
Vincenzo Maffione