On 1/5/16, 4:48 PM, "Stephen Hemminger" <stephen at networkplumber.org> wrote:
>On Tue, 5 Jan 2016 16:12:55 -0800
>Yong Wang <yongwang at vmware.com> wrote:
>
>> @@ -365,6 +366,14 @@ vmxnet3_xmit_pkts(void *tx_queue, struct rte_mbuf
>> **tx_pkts,
>> break;
>> }
>>
>> + if (rte_pktmbuf_pkt_len(txm) <= VMXNET3_HDR_COPY_SIZE) {
>> + struct Vmxnet3_TxDataDesc *tdd;
>> +
>> + tdd = txq->data_ring.base + txq->cmd_ring.next2fill;
>> + copy_size = rte_pktmbuf_pkt_len(txm);
>> + rte_memcpy(tdd->data, rte_pktmbuf_mtod(txm, char *),
>> copy_size);
>> + }
>
>Good idea to use a local region which optmizes the copy in the host,
>but this implementation needs to be more general.
>
>As written it is broken for multi-segment packets. A multi-segment
>packet will have a pktlen >= datalen as in:
> m -> mb_segs=3, pktlen=1200, datalen=200
> -> datalen=900
> -> datalen=100
>
>There are two ways to fix this. You could test for nb_segs == 1
>or better yet. Optimize each segment it might be that the first
>segment (or tail segment) would fit in the available data area.
Currently the vmxnet3 backend has a limitation of 128B data area so
it should work even for the multi-segmented pkt shown above. But
I agree it does not work for all multi-segmented packets. The
following packet will be such an example.
m -> nb_segs=3, pktlen=128, datalen=64
-> datalen=32
-> datalen=32
It?s unclear if/how we might get into such a multi-segmented pkt
but I agree we should handle this case. Patch updated taking the
simple approach (checking for nb_segs == 1). I?ll leave the
optimization as a future patch.
