dpdk

DPDK

Purpose

Guide agents through DPDK (Data Plane Development Kit): EAL initialization, poll-mode driver (PMD) concepts, rte_eth_rx_burst/tx_burst, mbuf mempools, rte_ring queues, huge page setup, RSS configuration, testpmd validation, QEMU virtio testing, and pipeline vs run-to-completion models.

When to Use

• Building a userspace packet forwarder bypassing the kernel network stack
• Achieving line-rate on 10/25/100 GbE NICs
• Prototyping NFV/vSwitch data plane components
• Testing NIC configuration with testpmd before custom code
• Comparing DPDK throughput with kernel networking or AF_XDP
• Running DPDK in VMs with virtio for development

Workflow

1. Huge pages setup

# 2MB hugepages (common)
echo 1024 | sudo tee /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages

# 1GB hugepages (better TLB perf on large memory)
echo 4 | sudo tee /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages

# Mount hugetlbfs
sudo mkdir -p /mnt/huge
sudo mount -t hugetlbfs nodev /mnt/huge

# Verify
grep Huge /proc/meminfo

DPDK EAL maps hugepages at startup — insufficient pages cause init failure.

2. EAL initialization

#include <rte_eal.h>
#include <rte_ethdev.h>

int main(int argc, char **argv) {
    int ret = rte_eal_init(argc, argv);
    if (ret < 0)
        rte_exit(EXIT_FAILURE, "EAL init failed\n");
    // argc/argv adjusted — remaining args for app
    return run_dataplane(argc - ret, argv + ret);
}

# Typical EAL args
./dpdk_app -l 0-3 -n 4 --huge-dir=/mnt/huge -- -p 0x3

# Flags:
# -l 0-3     — cores for DPDK (lcore mask)
# -n 4       — memory channels
# --proc-type=primary
# --file-prefix=myapp  — multi-instance

3. Port configuration and PMD

#include <rte_ethdev.h>

#define RX_RING_SIZE 1024
#define TX_RING_SIZE 1024
#define NUM_MBUFS    8191
#define MBUF_CACHE   250
#define BURST_SIZE   32

static const struct rte_eth_conf port_conf = {
    .rxmode = { .max_lro_pkt_size = RTE_ETHER_MAX_LEN },
};

struct rte_mempool *mbuf_pool;

int port_init(uint16_t port) {
    mbuf_pool = rte_pktmbuf_pool_create("MBUF_POOL", NUM_MBUFS,
        MBUF_CACHE, 0, RTE_MBUF_DEFAULT_BUF_SIZE, rte_socket_id());

    struct rte_eth_rxconf rxq_conf = dev_info.default_rxconf;
    ret = rte_eth_rx_queue_setup(port, 0, RX_RING_SIZE,
        rte_eth_dev_socket_id(port), &rxq_conf, mbuf_pool);
    // ... tx queue setup ...
    ret = rte_eth_dev_start(port);
    rte_eth_promiscuous_enable(port);
    return 0;
}