[dpdk-dev] [PATCH v12 1/6] ethdev: add Tx preparation

[Ananyev, Konstantin]

> 
> 2016-11-23 18:36, Tomasz Kulasek:
> > +/**
> > + * Process a burst of output packets on a transmit queue of an Ethernet device.
> > + *
> > + * The rte_eth_tx_prepare() function is invoked to prepare output packets to be
> > + * transmitted on the output queue *queue_id* of the Ethernet device designated
> > + * by its *port_id*.
> > + * The *nb_pkts* parameter is the number of packets to be prepared which are
> > + * supplied in the *tx_pkts* array of *rte_mbuf* structures, each of them
> > + * allocated from a pool created with rte_pktmbuf_pool_create().
> > + * For each packet to send, the rte_eth_tx_prepare() function performs
> > + * the following operations:
> > + *
> > + * - Check if packet meets devices requirements for tx offloads.
> > + *
> > + * - Check limitations about number of segments.
> > + *
> > + * - Check additional requirements when debug is enabled.
> > + *
> > + * - Update and/or reset required checksums when tx offload is set for packet.
> > + *
> > + * Since this function can modify packet data, provided mbufs must be safely
> > + * writable (e.g. modified data cannot be in shared segment).
> 
> I think we will have to remove this limitation in next releases.
> As we don't know how it could affect the API, I suggest to declare this
> API EXPERIMENTAL.

While I don't really mind to mart it as experimental, I don't really understand the reasoning:
Why " this function can modify packet data, provided mbufs must be safely writable" suddenly becomes a problem?
That seems like and obvious limitation to me and let say tx_burst() has the same one.
Second, I don't see how you are going to remove it without introducing a heavy performance impact.
Konstantin