Hi Gage, On Mon, Sep 14, 2020 at 04:11:53PM -0500, Gage Eads wrote: > 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 <gage.e...@intel.com> > --- > v3: Fixed "Title underline too short" warning > > v2: Added commit description > > doc/guides/mempool/index.rst | 1 + > doc/guides/mempool/stack.rst | 38 > +++++++++++++++++++++++++++++++++++ > doc/guides/prog_guide/mempool_lib.rst | 2 ++ > doc/guides/prog_guide/stack_lib.rst | 4 ++++ > 4 files changed, 45 insertions(+) > create mode 100644 doc/guides/mempool/stack.rst > > diff --git a/doc/guides/mempool/index.rst b/doc/guides/mempool/index.rst > index bbd02fd81..a0e55467e 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 000000000..bdf19cf04 > --- /dev/null > +++ b/doc/guides/mempool/stack.rst > @@ -0,0 +1,38 @@ > +.. 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. A stack-based mempool is often better suited to > +packet-processing workloads 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.
Would it make sense to give an example of a use-case where the stack driver should be used in place of the standard ring-based one? In most run-to-completion applications, the mbufs stay in per-core caches, so changing the mempool driver won't have a big impact. However, I suspect that for applications using a pipeline model (ex: rx on core0, tx on core1), the stack model would be more efficient. Is it something that you measured? If yes, it would be useful to explain this in the documentation. > + > +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 e3e1f940b..6f3c0067f 100644 > --- a/doc/guides/prog_guide/mempool_lib.rst > +++ b/doc/guides/prog_guide/mempool_lib.rst > @@ -105,6 +105,8 @@ 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 8fe8804e3..3097cab0c 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 > ------------------ > > -- > 2.13.6 >
