Hi, In the structure reorganization patchset [1], some work was done to ensure that the values of the following fields are always initialized for mbuf that are inside the mbuf pool (not yet allocated).
In other words, calling rte_mbuf_raw_alloc() or rte_mempool_get() return mbufs that are initialized as following: m->next = NULL m->nb_segs = 1 m->refcnt = 1 This property can be used in the Rx path of PMDs where the mbuf structure is filled from the hardware descriptors: the initialization of these fields can be skipped to gain few cycles per packet, and to avoid an access to the second cache line (m->next) before it is prefetched. It is advised to do this optimization in the PMDs for this reason, and also because we could want to move some of these fields to the second mbuf cache line in the future: accessing them in the Rx path would cost. This work has already been done at several places: http://dpdk.org/browse/dpdk/commit/?id=ebb7bcabb http://dpdk.org/browse/next/dpdk-next-net/commit/?id=e211a7569 http://dpdk.org/browse/next/dpdk-next-net/commit/?id=a37cf9005 http://dpdk.org/browse/next/dpdk-next-net/commit/?id=fb83a23ee ... Feel free to ask if you have any question. Thanks, Olivier [1] http://dpdk.org/ml/archives/dev/2017-April/063081.html
