Re: [dpdk-dev] [PATCH v2 0/5] Add non-blocking ring

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 15 Jan 2019 17:52:22 -0600
Gage Eads <gage.eads@intel.com> wrote:

> 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 limited to x86_64 machines.
> 
> 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 ABI and API changes; a deprecation notice will be
> posted in a separate commit.
> 
> This patchset depends on the non-blocking stack patchset[1].
> 
> [1] http://mails.dpdk.org/archives/dev/2019-January/123470.html
> 
> 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: change head and tail to pointer-width size
>   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 |   2 +-
>  drivers/mempool/ring/rte_mempool_ring.c         |  58 ++-
>  lib/librte_eventdev/rte_event_ring.h            |   6 +-
>  lib/librte_ring/Makefile                        |   2 +-
>  lib/librte_ring/meson.build                     |   2 +-
>  lib/librte_ring/rte_ring.c                      |  53 ++-
>  lib/librte_ring/rte_ring.h                      | 564 ++++++++++++++++++++++--
>  lib/librte_ring/rte_ring_generic.h              |  16 +-
>  lib/librte_ring/rte_ring_version.map            |   7 +
>  test/test/test_ring.c                           |  57 ++-
>  test/test/test_ring_perf.c                      |  19 +-
>  11 files changed, 699 insertions(+), 87 deletions(-)
> 

Just bumping the version number is not enough.
This looks like an ABI breakage for existing users.