RE: [PATCH v5 0/4] add pointer compression API

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> For some reason your email is not visible to me, even though it's in the
> archive.

No worries.

> 
> On 02/11/202416:32,Konstantin Ananyev konstantin.v.ananyev  wrote:
> 
> > From one side the code itself is very small and straightforward, > from other side - it is not clear to me what is intended usage for it
> > within DPDK and it's applianances?
> > Konstantin
> 
> The intended usage is explained in the cover email (see below) and demonstrated
> in the test supplied in the following patch - when sending arrays of pointers
> between cores as it happens in a forwarding example.

Yes, I saw that. The thing is that test is a 'synthetic' one.
My question was about how do you expect people to use it in more realistic scenarios?
Let say user has a bunch of mbuf pointers, possibly from different mempools.
How he can use this API: how to deduce the base pointer for all of them and what to
do if it can't be done?
 
> On 01/11/2023 18:12, Paul Szczepanek wrote:
> 
> > This patchset is proposing adding a new EAL header with utility functions
> > that allow compression of arrays of pointers.
> >
> > When passing caches full of pointers between threads, memory containing
> > the pointers is copied multiple times which is especially costly between
> > cores. A compression method will allow us to shrink the memory size
> > copied.
> >
> > The compression takes advantage of the fact that pointers are usually
> > located in a limited memory region (like a mempool). We can compress them
> > by converting them to offsets from a base memory address.
> >
> > Offsets can be stored in fewer bytes (dictated by the memory region size
> > and alignment of the pointer). For example: an 8 byte aligned pointer
> > which is part of a 32GB memory pool can be stored in 4 bytes. The API is
> > very generic and does not assume mempool pointers, any pointer can be
> > passed in.
> >
> > Compression is based on few and fast operations and especially with vector
> > instructions leveraged creates minimal overhead.
> >
> > The API accepts and returns arrays because the overhead means it only is
> > worth it when done in bulk.
> >
> > Test is added that shows potential performance gain from compression. In
> > this test an array of pointers is passed through a ring between two cores.
> > It shows the gain which is dependent on the bulk operation size. In this
> > synthetic test run on ampere altra a substantial (up to 25%) performance
> > gain is seen if done in bulk size larger than 32. At 32 it breaks even and
> > lower sizes create a small (less than 5%) slowdown due to overhead.
> >
> > In a more realistic mock application running the l3 forwarding dpdk
> > example that works in pipeline mode on two cores this translated into a
> > ~5% throughput increase on an ampere altra.
> >
> > v2:
> > * addressed review comments (style, explanations and typos)
> > * lowered bulk iterations closer to original numbers to keep runtime short
> > * fixed pointer size warning on 32-bit arch
> > v3:
> > * added 16-bit versions of compression functions and tests
> > * added documentation of these new utility functions in the EAL guide
> > v4:
> > * added unit test
> > * fix bug in NEON implementation of 32-bit decompress
> > v5:
> > * disable NEON and SVE implementation on AARCH32 due to wrong pointer size
> >
> > Paul Szczepanek (4):
> >    eal: add pointer compression functions
> >    test: add pointer compress tests to ring perf test
> >    docs: add pointer compression to the EAL guide
> >    test: add unit test for ptr compression
> >
> >   .mailmap                                      |   1 +
> >   app/test/meson.build                          |   1 +
> >   app/test/test_eal_ptr_compress.c              | 108 ++++++
> >   app/test/test_ring.h                          |  94 ++++-
> >   app/test/test_ring_perf.c                     | 354 ++++++++++++------
> >   .../prog_guide/env_abstraction_layer.rst      | 142 +++++++
> >   lib/eal/include/meson.build                   |   1 +
> >   lib/eal/include/rte_ptr_compress.h            | 266 +++++++++++++
> >   8 files changed, 843 insertions(+), 124 deletions(-)
> >   create mode 100644 app/test/test_eal_ptr_compress.c
> >   create mode 100644 lib/eal/include/rte_ptr_compress.h
> >
> > --
> > 2.25.1
> >