From 1fb6301ccbb845f344f276ea2db64dda882e196d Mon Sep 17 00:00:00 2001 From: Gage Eads Date: Wed, 7 Oct 2020 09:18:32 -0500 Subject: [PATCH] doc: add stack mempool guide This guide describes the two stack modes, their tradeoffs, and (via a reference to the mempool guide) how to enable them. Signed-off-by: Gage Eads Reviewed-by: Olivier Matz --- doc/guides/mempool/index.rst | 1 + doc/guides/mempool/stack.rst | 43 +++++++++++++++++++++++++++ doc/guides/prog_guide/mempool_lib.rst | 2 ++ doc/guides/prog_guide/stack_lib.rst | 4 +++ 4 files changed, 50 insertions(+) create mode 100644 doc/guides/mempool/stack.rst diff --git a/doc/guides/mempool/index.rst b/doc/guides/mempool/index.rst index bbd02fd811..a0e55467e6 100644 --- a/doc/guides/mempool/index.rst +++ b/doc/guides/mempool/index.rst @@ -14,3 +14,4 @@ application through the mempool API. octeontx octeontx2 ring + stack diff --git a/doc/guides/mempool/stack.rst b/doc/guides/mempool/stack.rst new file mode 100644 index 0000000000..ab71716bdf --- /dev/null +++ b/doc/guides/mempool/stack.rst @@ -0,0 +1,43 @@ +.. SPDX-License-Identifier: BSD-3-Clause + Copyright(c) 2020 Intel Corporation. + +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 :ref:`Mempool_Handlers`: + +- ``stack`` + + The underlying **rte_stack** operates in standard (lock-based) mode. + For more information please refer to :ref:`Stack_Library_Std_Stack`. + +- ``lf_stack`` + + The underlying **rte_stack** operates in lock-free mode. For more + information please refer to :ref:`Stack_Library_LF_Stack`. + +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, by design, is 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. + +For a more detailed description of the stack implementations, please refer to +:doc:`../prog_guide/stack_lib`. diff --git a/doc/guides/prog_guide/mempool_lib.rst b/doc/guides/prog_guide/mempool_lib.rst index f0bdcd3be1..890535eb23 100644 --- a/doc/guides/prog_guide/mempool_lib.rst +++ b/doc/guides/prog_guide/mempool_lib.rst @@ -104,6 +104,8 @@ These user-owned caches can be explicitly passed to ``rte_mempool_generic_put()` The ``rte_mempool_default_cache()`` call returns the default internal cache if any. In contrast to the default caches, user-owned caches can be used by unregistered non-EAL threads too. +.. _Mempool_Handlers: + Mempool Handlers ------------------------ diff --git a/doc/guides/prog_guide/stack_lib.rst b/doc/guides/prog_guide/stack_lib.rst index 8fe8804e38..3097cab0c2 100644 --- a/doc/guides/prog_guide/stack_lib.rst +++ b/doc/guides/prog_guide/stack_lib.rst @@ -28,6 +28,8 @@ Implementation The library supports two types of stacks: standard (lock-based) and lock-free. Both types use the same set of interfaces, but their implementations differ. +.. _Stack_Library_Std_Stack: + Lock-based Stack ---------------- @@ -35,6 +37,8 @@ The lock-based stack consists of a contiguous array of pointers, a current index, and a spinlock. Accesses to the stack are made multi-thread safe by the spinlock. +.. _Stack_Library_LF_Stack: + Lock-free Stack ------------------ -- 2.20.1