PacketFive | Cnuas Virtual AI/HPC Infrastructure
CnuasSHMEM, Datasheet
Partitioned global address space library over the CnuasLink fabric
Document DS-CNU-018  Revision A  Issued 03 August 2026  Status Preview, not implemented
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  Item     Value
  -------- --------------------------------------------------------
  Part     CnuasSHMEM
  Type     Partitioned global address space communication library
  Models   NVIDIA NVSHMEM
  Status   Preview, specified but not implemented
  Repo     PacketFive/CnuasGPU

PREVIEW DATASHEET

CnuasSHMEM carries no implementation in the tree. No symmetric heap, no one
sided operations and no signalling exist. This datasheet records the specified
design.

1. Overview

CnuasSHMEM is the intended one sided communication library for CnuasGPU. Where
CnuasCCL provides collective operations that every rank enters together,
CnuasSHMEM lets one accelerator read and write another accelerator's memory
without the remote side taking part, which suits irregular and latency
sensitive access patterns.

2. Specified operations

  Group                     Operations
  ------------------------- -------------------------------
  One sided data movement   Put, get
  Atomics                   Remote read modify write
  Signalling                Set and wait on a remote flag

3. Transport

  Item                Specified value
  ------------------- ---------------------------------------------------------------------------
  Primary transport   CnuasLink, accelerator to accelerator
  Address space       Symmetric heap across participating accelerators, not specified in detail
  Underlying path     The accelerator fabric rings described in Kernel Modules section 5

4. Dependencies

  Requirement                              Status
  ---------------------------------------- --------------------------------
  CnuasLink transport                      Implemented
  Remote memory addressing model           Not specified
  Device side calls from within a kernel   Not implemented, needs CnuasCC
  Atomic operation support on the fabric   Not implemented

Note that one sided operations issued from inside a kernel, which is the usual
NVSHMEM pattern, need a device compiler. Host initiated operations could land
earlier, and that split has not yet been decided.

5. Interim position

Applications needing one sided semantics today should use RDMA verbs directly
through the verbs provider, which supports remote write, remote read and
atomic operations over the network fabric.

6. Revision history

  Revision   Notes
  ---------- ------------------------------------------------------------------------------------------------------
  A          First publication as a preview. Operation list taken from the CnuasGPU design document, section 7.6.

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PacketFive, Packet Five Networks Ltd., Dublin, Ireland.
Cnuas Virtual AI/HPC Infrastructure is published at https://github.com/PacketFive/cnuas under the
Apache License 2.0; read it at https://github.com/PacketFive/cnuas/blob/main/LICENSE.
Cnuas Virtual AI/HPC Infrastructure is emulation software. It is not affiliated with, endorsed by, or derived
from any hardware vendor, and every device it models is a software artefact.
The work is published by its authors in a personal capacity and is not
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Specifications describe the referenced revision of the software and may
change without notice. Contact info@packetfive.com.