[dpdk-dev] [PATCH v4 0/5] Add non-blocking ring

[Gage Eads]

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 non-blocking ring, on top of which a mempool can run.
Crucially, the non-blocking algorithm relies on a 128-bit compare-and-swap, so
it is currently limited to x86_64 machines. This is also an experimental API,
so RING_F_NB users must build with the ALLOW_EXPERIMENTAL_API flag.

The ring uses more compare-and-swap atomic operations than the regular rte ring:
With no contention, an enqueue of n pointers uses (1 + 2n) CAS operations and a
dequeue of n pointers uses 2. 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 non-blocking ring's.
- Software caching can mitigate the average case performance for ring-based
  algorithms. For example, a non-blocking ring based mempool (a likely use case
  for this ring) with per-thread caching.

The non-blocking ring is enabled via a new flag, RING_F_NB. For ease-of-use,
existing ring enqueue/dequeue functions work with both "regular" and
non-blocking rings.

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

This patchset makes one API change; a deprecation notice will be posted in a
separate commit.

This patchset depends on the 128-bit compare-and-set patch[1].

[1] http://mails.dpdk.org/archives/dev/2019-January/124159.html

v4:
 - 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

v3:
 - 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.

v2:
 - 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 (5):
  ring: add 64-bit headtail structure
  ring: add a non-blocking implementation
  test_ring: add non-blocking ring autotest
  test_ring_perf: add non-blocking ring perf test
  mempool/ring: add non-blocking ring handlers

 doc/guides/prog_guide/env_abstraction_layer.rst |   5 +
 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                      |  72 +++-
 lib/librte_ring/rte_ring.h                      | 336 +++++++++++++++++--
 lib/librte_ring/rte_ring_c11_mem.h              | 427 ++++++++++++++++++++++++
 lib/librte_ring/rte_ring_generic.h              | 408 ++++++++++++++++++++++
 lib/librte_ring/rte_ring_version.map            |   7 +
 test/test/test_ring.c                           |  57 ++--
 test/test/test_ring_perf.c                      |  19 +-
 11 files changed, 1319 insertions(+), 73 deletions(-)

-- 
2.13.6