[dpdk-dev] Couple of PMD questions

[Jay Rolette]

On Wed, Apr 20, 2016 at 4:35 AM, Andriy Berestovskyy <aber at semihalf.com>
wrote:

> Hi Jay,
>
> On Tue, Apr 19, 2016 at 10:16 PM, Jay Rolette <rolette at infinite.io> wrote:
> > Should the driver error out in that case instead of only "sort of"
> working?
>
> +1, we hit the same issue. Error or log message would help.
>
> > If I support a max frame size of 9216 bytes (exactly a 1K multiple to
> make
> > the NIC happy), then max_rx_pkt_len is going to be 9216 and
> data_room_size
> > will be 9216 + RTE_PKTMBUF_HEADROOM.
>
> Try to set max_rx_pkt_len <= 9K - 8 and mempool element size to 9K +
> headroom + size of structures.
>

Thanks, Andriy. That makes sense given how the code + NIC are working.


> > Is that check correct?
>
> Datasheet says:
> The MFS does not include the 4 bytes of the VLAN header. Packets with
> VLAN header can be as large as MFS + 4. When double VLAN is enabled,
> the device adds 8 to the MFS for any packets.
>

Gotcha. Hopefully we can get the docs and example code up to where app
developers don't need to crawl through driver source and NIC datasheets.
That or have rte_pktmbuf_pool_create() take care of that sort of detail
automatically. :-)

Jay


Regards,
> Andriy
>