Re: Can I use rte_pktmbuf_chain to chain multiple mbuffs for calling only single tx_eth_burst API

[Ansar Kannankattil <ansarkannankat@gmail.com>]

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Thanks for the responses,
Then what is the advantage of chaining mbuffs over using the mbuff array?

On Thu, Feb 10, 2022 at 2:26 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 2/9/2022 10:46 PM, Stephen Hemminger wrote:
> > On Wed, 9 Feb 2022 22:18:24 +0000
> > Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> >
> >> On 2/9/2022 6:03 PM, Ansar Kannankattil wrote:
> >>> Hi
> >>> My intention is to decrease the number of rte_tx_eth_burst calls, I
> know that mentioning nb_pkts will result in sending multiple packets in a
> single call.
> >>> But providing nb_pkts=1 and posting a head mbuff having number of
> mbuffs linked with it will results sending multiple packets
> >>
> >> If driver supports, you can do it.
> >> Driver should expose this capability via RTE_ETH_TX_OFFLOAD_MULTI_SEGS
> flag,
> >> in 'dev_info->tx_offload_capa'.
> >>
> >>> If not, what is the use case of linking multiple mbuffs together
> >>
> >> It is also used in Rx path (again if driver supports).
> >
> > I think Ansar was asking about chaining multiple packets in one call to
> tx burst.
> > The chaining in DPDK is to make a single packet out of multiple pieces
> (like writev).
> >
> > DPDK mbufs were based on original BSD concept.
> > In BSD mbufs, mbuf has two linked lists.
> >    BSD m->m_next pointer == DPDK m->next  for multiple parts of packet.
> >    BSD m->m_nextpkt                       for next packet in queue
> >
> > There is no nextpkt in DPDK.
>
> Right, chaining mbufs is for segmented packets.
>

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