Hi Olivier, > -----Original Message----- > From: Olivier Matz [mailto:olivier.m...@6wind.com] > Sent: Friday, December 2, 2016 8:24 AM > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > Cc: Thomas Monjalon <thomas.monja...@6wind.com>; Kulasek, TomaszX > <tomaszx.kula...@intel.com>; dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH v12 1/6] ethdev: add Tx preparation > > Hi Konstantin, > > On Fri, 2 Dec 2016 01:06:30 +0000, "Ananyev, Konstantin" > <konstantin.anan...@intel.com> wrote: > > > > > > 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 > > > > About tx_burst(), I don't think we should force the user to provide a > writable mbuf. There are many use cases where passing a clone > already works as of today and it avoids duplicating the mbuf data. For > instance: traffic generator, multicast, bridging/tap, etc... > > Moreover, this requirement would be inconsistent with the model you are > proposing in case of pipeline: > - tx_prepare() on core X, may update the data > - tx_burst() on core Y, should not touch the data to avoid cache misses >
Probably I wasn't very clear in my previous mail. I am not saying that we should force the user to pass a writable mbuf. What I am saying that for tx_burst() current expectation is that after mbuf is handled to tx_burst() user shouldn't try to modify its buffer contents till TX engine is done with the buffer (mbuf_free() is called by TX func for it). For tx_prep(), I think, it is the same though restrictions are a bit more strict: user should not try to read/write to the mbuf while tx_prep() is not finished with it. What puzzles me is that why that should be the reason to mark tx_prep() as experimental. Konstantin
