2022-01-29 18:46 (UTC-0500), fwefew 4t4tg: [...] > 1. Does cache_size include or exclude data_room_size? > 2. Does cache_size include or exclude sizeof(struct rtre_mbuf)? > 3. Does cache size include or exclude RTE_PKTMBUF_HEADROOM?
Cache size is measured in the number of elements, irrelevant of their size. It is not a memory size, so the questions above are not really meaningful. > 4. What lcore is the allocated memory pinned to? Memory is associated with a NUMA node (DPDK calls it "socket"), not an lcore. Each lcore belongs to one NUMA node, see rte_lcore_to_socket_id(). > The lcore of the caller > when this method is run? The answer here is important. If it's the lcore of > the caller when called, this routine should be called in the lcore's entry > point so it's on the right lcore the memory is intended. Calling it on the > lcore that happens to be running main, for example, could have a bad side > effect if it's different from where the memory will be ultimately used. The NUMA node is controlled by "socket_id" parameter. Your considerations are correct, often you should create separate mempools for each NUMA node to avoid this performance issue. (You should also consider which NUMA node each device belongs to.) > 5. Which one of the formal arguments represents tail room indicated in > https://doc.dpdk.org/guides/prog_guide/mbuf_lib.html#figure-mbuf1 [...] > 5. Unknown. Perhaps if you want private data which corresponds to tail room > in the diagram above one has to call rte_mempool_create() instead and focus > on private_data_size. Incorrect; tail room is simply an unused part at the end of the data room. Private data is for the entire mempool, not for individual mbufs. > Mempool creation is like malloc: you request the total number of absolute > bytes required. The API will not add or remove bytes to the number you > specify. Therefore the number you give must be inclusive of all needs > including your payload, any DPDK overheader, headroom, tailroom, and so on. > DPDK is not adding to the number you give for its own purposes. Clearer? > Perhaps ... but what needs? Read on ... On the contrary: rte_pktmbuf_pool_create() takes the amount of usable memory (dataroom) and adds space for rte_mbuf and the headroom. Furthermore, the underlying rte_mempool_create() ensures element (mbuf) alignment, may spread the elements between pages, etc. [...] > No. I might not. I might have half my TXQ and RXQs dealing with tiny > mbufs/packets, and the other half dealing with completely different traffic > of a completely different size and structure. So I might want memory pool > allocation to be done on a smaller scale e.g. per RXQ/TXQ/lcore. DPDK > doesn't seem to permit this. You can create different mempools for each purpose and specify the proper mempool to rte_eth_rx_queue_setup(). When creating them, you can and should also take NUMA into account. Take a look at init_mem() function of examples/l3fwd.
