On Tue, 14 Jul 2020 08:31:32 +0100
"Kinsella, Ray" [off-list ref] wrote:

On 13/07/2020 23:19, Stephen Hemminger wrote:

quoted

On Mon, 13 Jul 2020 12:11:19 +0100
Vladimir Medvedkin [off-list ref] wrote:
  

quoted

This patch series implements vectorized lookup using AVX512 for
ipv4 dir24_8 and ipv6 trie algorithms.
Also introduced rte_fib_set_lookup_fn() to change lookup function type.
Added option to select lookup function type in testfib application.

v6:
 - style fixes

v5:
 - prefix zmm macro in rte_vect.h with RTE_X86
 - remove unnecessary typedef for _x86_zmm_t
 - reword commit title
 - fix typos

v4:
 - use __rte_aligned() instead of using compiler attribute directly
 - rework and add comments to meson.build

v3:
 - separate out the AVX-512 code into a separate file

v2:
 - rename rte_zmm to __rte_x86_zmm to reflect its internal usage
 - make runtime decision to use avx512 lookup

Vladimir Medvedkin (8):
  eal/x86: introduce AVX 512-bit type
  fib: make lookup function type configurable
  fib: move lookup definition into the header file
  fib: introduce AVX512 lookup
  fib6: make lookup function type configurable
  fib6: move lookup definition into the header file
  fib6: introduce AVX512 lookup
  app/testfib: add support for different lookup functions

 app/test-fib/main.c                   |  58 +++++-
 lib/librte_eal/x86/include/rte_vect.h |  19 ++
 lib/librte_fib/Makefile               |  24 +++
 lib/librte_fib/dir24_8.c              | 281 +++++---------------------
 lib/librte_fib/dir24_8.h              | 226 ++++++++++++++++++++-
 lib/librte_fib/dir24_8_avx512.c       | 165 +++++++++++++++
 lib/librte_fib/dir24_8_avx512.h       |  24 +++
 lib/librte_fib/meson.build            |  31 +++
 lib/librte_fib/rte_fib.c              |  21 +-
 lib/librte_fib/rte_fib.h              |  24 +++
 lib/librte_fib/rte_fib6.c             |  20 +-
 lib/librte_fib/rte_fib6.h             |  22 ++
 lib/librte_fib/rte_fib_version.map    |   2 +
 lib/librte_fib/trie.c                 | 161 +++------------
 lib/librte_fib/trie.h                 | 119 ++++++++++-
 lib/librte_fib/trie_avx512.c          | 269 ++++++++++++++++++++++++
 lib/librte_fib/trie_avx512.h          |  20 ++
 17 files changed, 1114 insertions(+), 372 deletions(-)
 create mode 100644 lib/librte_fib/dir24_8_avx512.c
 create mode 100644 lib/librte_fib/dir24_8_avx512.h
 create mode 100644 lib/librte_fib/trie_avx512.c
 create mode 100644 lib/librte_fib/trie_avx512.h
 

Did anyone else see the recent AVX512 discussion from Linus:
  "I hope AVX512 dies a painful death, and that Intel starts fixing real problems 
   instead of trying to create magic instructions to then create benchmarks that they can look good on.   

Yup - I saw this one.
Sweeping statements like these are good to provoke debate, the truth is generally more nuanced.
If you continue to read the post, Linus appears to be mostly questioning microprocessor design decisions.

That is an interesting discussion, however the reality is that the technology does exists and may be beneficial for Packet Processing. 

I would suggest, we continue to apply the same logic governing adoption of any technology by DPDK. 
When the technology is present and a clear benefit is shown, we use it with caution.

In the case of Vladimir's patch,
the user has to explicitly switch on the AVX512 lookup with RTE_FIB_DIR24_8_VECTOR_AVX512.

Using what is available makes sense in DPDK.