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

[Xie, Huawei]

On 10/27/2015 10:23 AM, Stephen Hemminger wrote:
> You need to use the extended mergeable rx buffer format.
> It is a virtio spec requirement, look at Linux virtio network driver
> or ask the virtio maintainers for Linux
> if you need more clarification.
Yes, it is spec requirement as far as we know though num_buffers might
not be used.
So far not a big deal for us. Let us get clarification from mst later.
>
> On Tue, Oct 27, 2015 at 10:56 AM, Xie, Huawei <huawei.xie at intel.com
> <mailto:huawei.xie at intel.com>> wrote:
>
>     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
>     <mailto: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.
>     >
>     >
>
>