[dpdk-dev] [PATCH v2 0/5] virtio: Tx performance improvements

[Xie, Huawei]

On 10/27/2015 7:52 AM, Stephen Hemminger wrote:
> On Fri, 23 Oct 2015 09:00:38 +0000
> "Xie, Huawei" <huawei.xie at intel.com> wrote:
>
>>>> Why use merge-able rx header here in the tx region?  
>>> If mergeable rx is negotiated then the header must be used for
>>> both Tx and Rx. I chose to allocate the largest possible header
>>> needed, rather than having to deal with variable size data structure.  
>> Our original code is also using merge-able header for TX descriptor if
>> this negotiated.
>> I checked the virtio spec, all of the merge-able header is about
>> receiving buffers, which is expected. That is why i feel weird here.
>> Maybe not a big deal?
> Since num_buffers is only in merge-able header, the negotiation is implied
> to be symmetric.
>
Can we come to the conclusion that in tx case, we use merge-able header
though number_buffers is not used at all?
> Reading 0.95 spec 
>
> Under "Packet Transmission"
>  3. If the driver negotatied the VIRTIO_NET_F_MGR_RXBUF feature
>     the num_buffers field is set to zero.
>
>