[dpdk-dev] rte_prefetch0() performance info

[Parikshith Chowdaiah <pchowdai@gmail.com>]

Hi all,
I have a question related to usage of rte_prefetch0() function,In one of
the sample files, we have implementation like:

            /* Prefetch first packets */

            for (j = 0; j < PREFETCH_OFFSET && j < nb_rx; j++) {

                rte_prefetch0(rte_pktmbuf_mtod(

                        pkts_burst[j], void *));

            }



            /* Prefetch and forward already prefetched packets */

            for (j = 0; j < (nb_rx - PREFETCH_OFFSET); j++) {

                rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[

                        j + PREFETCH_OFFSET], void *));

                l3fwd_simple_forward(pkts_burst[j], portid,

                                qconf);

            }



            /* Forward remaining prefetched packets */

            for (; j < nb_rx; j++) {

                l3fwd_simple_forward(pkts_burst[j], portid,

                                qconf);

            }


where the prefetch0() is carried out in multiple split iterations, would
like to have an insight on whether it makes performance improvement to
likes of:



       for (j = 0; j  < nb_rx; j++) {

                rte_prefetch0(rte_pktmbuf_mtod(

                        pkts_burst[j], void *));

            }


and how frequent rte_prefetch() needs to called for the same packet. and
any mechanisms to call in bulk for 64 packets at once ?


thanks

Parikshith