4. Stack Mempool Driver

rte_mempool_stack is a pure software mempool driver based on the rte_stack DPDK library. For run-to-completion workloads with sufficiently large per-lcore caches, the mbufs will likely stay in the per-lcore caches and the mempool type (ring, stack, etc.) will have a negligible impact on performance. However a stack-based mempool is often better suited to pipelined packet-processing workloads (which allocate and free mbufs on different lcores) than a ring-based mempool, since its LIFO behavior results in better temporal locality and a minimal memory footprint even if the mempool is over-provisioned. Users are encouraged to benchmark with multiple mempool types to determine which works best for their specific application.

The following modes of operation are available for the stack mempool driver and can be selected as described in Mempool Handlers:

• stack

  The underlying rte_stack operates in standard (lock-based) mode. For more information please refer to Lock-based stack.

• lf_stack

  The underlying rte_stack operates in lock-free mode. For more information please refer to Lock-free stack.

• pile

  The underlying rte_stack operates in lock-free mode, and is optimized for bulks of objects. For more information please refer to Pile.

The standard stack outperforms the lock-free stack on average, however the standard stack is non-preemptive: if a mempool user is preempted while holding the stack lock, that thread will block all other mempool accesses until it returns and releases the lock. As a result, an application using the standard stack whose threads can be preempted can suffer from brief, infrequent performance hiccups.

The lock-free stack and the pile, by design, are not susceptible to this problem; one thread can be preempted at any point during a push or pop operation and will not impede the progress of any other thread.

The pile is not LIFO per object, but per bulk of objects. Although the pile is optimized for bulks of objects, it can handle any request size.

For a more detailed description of the stack implementations, please refer to Stack Library.