On 14-Nov-18 5:45 AM, Sam wrote:
OK, then shortly speaking, DPDK will NOT care about padding.
NIC will care about padding while send and recv with NIC.
kernel will care about while send and recv with vhostuser port.
Is that right?
I cannot speak for virtio/vhost user since i am not terribly familiar
with them. For regular packets, generally speaking, packets shorter than
60 bytes are invalid. Whether DPDK does or does not care about padding
is irrelevant, because *you* are attempting to transmit packets that are
not valid. You shouldn't rely on this behavior.
Burakov, Anatoly <anatoly.bura...@intel.com
<mailto:anatoly.bura...@intel.com>> 于2018年11月13日周二 下午5:29写道：
On 13-Nov-18 7:16 AM, Sam wrote:
> Hi all,
>
> As we know, ethernet frame must longer then 64B.
>
> So if I create rte_mbuf and fill it with just 60B data, will
> rte_eth_tx_burst add padding data, let the frame longer then 64B
>
> If it does, where is the code?
>
Others can correct me if i'm wrong here, but specifically in case of
64-byte packets, these are the shortest valid packets that you can
send,
and a 64-byte packet will actually carry only 60 bytes' worth of packet
data, because there's a 4-byte CRC frame at the end (see Ethernet frame
format). If you enabled CRC offload, then your NIC will append the 4
bytes at transmit. If you haven't, then it's up to each individual
driver/NIC to accept/reject such a packet because it can rightly be
considered malformed.
In addition, your NIC may add e.g. VLAN tags or other stuff, again
depending on hardware offloads that you have enabled in your TX
configuration, which may push the packet size beyond 64 bytes while
having only 60 bytes of actual packet data.
--
Thanks,
Anatoly
--
Thanks,
Anatoly
