[dpdk-dev] [PATCH v6 0/6] Add lock-free ring and mempool handler

Gage Eads gage.eads at intel.com
Wed Mar 6 16:03:36 CET 2019

For some users, the rte ring's "non-preemptive" constraint is not acceptable;
for example, if the application uses a mixture of pinned high-priority threads
and multiplexed low-priority threads that share a mempool.

This patchset introduces a lock-free ring and a mempool based on it. The
lock-free algorithm relies on a double-pointer compare-and-swap, so for 64-bit
architectures it is currently limited to x86_64.

The ring uses more compare-and-swap atomic operations than the regular rte ring:
With no contention, an enqueue of n pointers uses (1 + n) CAS operations and a
dequeue of n pointers uses 1. This algorithm has worse average-case performance
than the regular rte ring (particularly a highly-contended ring with large bulk
accesses), however:
- For applications with preemptible pthreads, the regular rte ring's worst-case
  performance (i.e. one thread being preempted in the update_tail() critical
  section) is much worse than the lock-free ring's.
- Software caching can mitigate the average case performance for ring-based
  algorithms. For example, a lock-free ring based mempool (a likely use case
  for this ring) with per-thread caching.

The lock-free ring is enabled via a new flag, RING_F_LF. For ease-of-use,
existing ring enqueue/dequeue functions work with both standard and lock-free
rings. This is also an experimental API, so RING_F_LF users must build with the

This patchset also adds lock-free versions of ring_autotest and
ring_perf_autotest, and a lock-free ring based mempool.

This patchset makes one API change; a deprecation notice was posted in a
separate commit[1].

This patchset depends on the 128-bit compare-and-set patch[2].

[1] http://mails.dpdk.org/archives/dev/2019-February/124321.html
[2] http://mails.dpdk.org/archives/dev/2019-March/125751.html

- Rebase patchset onto master (test/test/ -> app/test/)

 - Incorporated lfring's enqueue and dequeue logic from
 - Renamed non-blocking -> lock-free and NB -> LF to align with a similar
   change in the lock-free stack patchset:
 - Added support for 32-bit architectures by using the full 32b of the
   modification counter and requiring LF rings on these architectures to be at
   least 1024 entries.
 - Updated to the latest rte_atomic128_cmp_exchange() interface.
 - Added ring start marker to struct rte_ring

 - Split out nb_enqueue and nb_dequeue functions in generic and C11 versions,
   with the necessary memory ordering behavior for weakly consistent machines.
 - Convert size_t variables (from v2) to uint64_t and no-longer-applicable
   comment about variably-sized ring indexes.
 - Fix bug in nb_enqueue_mp that the breaks the non-blocking guarantee.
 - Split the ring_ptr cast into two lines.
 - Change the dependent patchset from the non-blocking stack patch series
   to one only containing the 128b CAS commit

 - Avoid the ABI break by putting 64-bit head and tail values in the same
   cacheline as struct rte_ring's prod and cons members.
 - Don't attempt to compile rte_atomic128_cmpset without
   ALLOW_EXPERIMENTAL_API, as this would break a large number of libraries.
 - Add a helpful warning to __rte_ring_do_nb_enqueue_mp() in case someone tries
   to use RING_F_NB without the ALLOW_EXPERIMENTAL_API flag.
 - Update the ring mempool to use experimental APIs
 - Clarify that RINB_F_NB is only limited to x86_64 currently; e.g. ARMv8 has the
   ISA support for 128-bit CAS to eventually support it.

 - Merge separate docs commit into patch #5
 - Convert uintptr_t to size_t
 - Add a compile-time check for the size of size_t
 - Fix a space-after-typecast issue
 - Fix an unnecessary-parentheses checkpatch warning
 - Bump librte_ring's library version

Gage Eads (6):
  ring: add a pointer-width headtail structure
  ring: add a ring start marker
  ring: add a lock-free implementation
  test_ring: add lock-free ring autotest
  test_ring_perf: add lock-free ring perf test
  mempool/ring: add lock-free ring handlers

 app/test/test_ring.c                            |  61 +--
 app/test/test_ring_perf.c                       |  19 +-
 doc/guides/prog_guide/env_abstraction_layer.rst |  10 +
 drivers/mempool/ring/Makefile                   |   1 +
 drivers/mempool/ring/meson.build                |   2 +
 drivers/mempool/ring/rte_mempool_ring.c         |  58 ++-
 lib/librte_ring/rte_ring.c                      |  92 ++++-
 lib/librte_ring/rte_ring.h                      | 334 ++++++++++++++--
 lib/librte_ring/rte_ring_c11_mem.h              | 501 ++++++++++++++++++++++++
 lib/librte_ring/rte_ring_generic.h              | 484 +++++++++++++++++++++++
 lib/librte_ring/rte_ring_version.map            |   7 +
 11 files changed, 1492 insertions(+), 77 deletions(-)


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