openpower/ISA_WG/Board_letter_26mar2021.mdwn

   1 # Draft letter
   2
   3 * letter to OpenPOWER Foundation Board of Directors
   4 * purpose: dialog on how LibreSOC and RED Semiconductor propose extensions
   5
   6 edit history:
   7
   8 * 25mar2021 first revision
   9
  10 to be sent to:
  11
  12 * OPF Board board@openpowerfoundation.org
  13 * Tim Ansell blog@mithis.com
  14 * Toshaan Bharvani
  15 * James Kulina
  16 * Mendy
  17 * cc Alain Williams
  18 * cc David Calderwood
  19 * cc Paul Mackerras
  20
  21 # Contents
  22
  23 Dear OPF Board,
  24
  25 As you know the LibreSOC team have been working for over 3 years on a massive conceptual upgrade to the OpenPOWER ISA, based on Cray-Style Vectors, which will modernise it for today's 3D and VPU workloads, with an incidental side-effect of upgrading it for future supercomputing needs over the next few decades in a clean and elegant fashion.  RISC-V has RVV, ARM has SVE2, x86 has AVX512, whilst OpenPOWER has an out-of-date SIMD ISA. It goes without saying that over the decades, SIMD has been demonstrated to be harmful.
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  27 https://www.sigarch.org/simd-instructions-considered-harmful/
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  29 Normally, such huge ISA development efforts would be instigated, organised and funded through either Academia or an extremely large Corporation, or a Consortium combining multiple such entities.  It is therefore without precedent across the Computing Industry for something of this magnitude of effort to come not only from *individuals* with a completely independent non-affiliated Libre background but from a Libre background that is funded by a Charitable Foundation with a mandate to only fund "Works for the Public Good" (NLnet).
  30
  31 From reading the PowerISA v3.0C sections we have learned and taken on board that a "Sandbox" opcode exists (EXT22) which is intended for "small private extensions" to the OpenPOWER ISA.  Our Bitmanipulation Extension alone, needed for Audio/Video and cryptographic workloads, struggles to fit into that space, and we have not yet added Custom 3D opcodes or the IEEE754 Transcendentals (SIN, COS).
  32
  33 http://libre-soc.org/openpower/bitmanip
  34
  35 More than that, these are all "general-purpose" opcodes with uses far beyond LibreSOC's use-case: notwithstanding LibreSOC's use-case itself being by definition general-purpose.  The instructions in the PowerISA v3.0C document therefore *require* us to contact the OpenPOWER Foundation, to initiae the process of including our opcodes, and SVP64, in the OpenPOWER ISA.
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  38 In speaking with various people (Toshaan, Paul and Hugh) we have pieced together the way that the Op
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  40