NCCL 2.28.3-1

Device API (Experimental)
 * Introduces device-side APIs to integrate NCCL communication directly into application kernels.
 * Supports LSA (Load/Store Access) for CUDA P2P communication over NVLink and some PCIe platforms.
 * Supports Multimem for hardware multicast using NVLink SHARP.
 * Adds initial framework for GIN (GPU-Initiated Networking), currently under development.
 * Introduces device communicators created using ncclDevCommCreate.
 * Enables device-side communication operations with synchronization (ncclLsaBarrierSession) and memory accessors (ncclGetLsaPointer, ncclGetLsaMultimemPointer).
 * Experimental APIs - signatures and functionality may evolve in future releases.
 * No ABI compatibility is guaranteed — applications must be recompiled with each new NCCL release.

Symmetric memory improvements
 * Support for aggregating symmetric operations using ncclGroupStart/End APIs.
 * Reimplement symmetric kernels using device API.

New Host APIs
 * Introduce new host collective APIs: ncclAlltoAll, ncclScatter, ncclGather.

CE (Copy Engine) Collectives
 * Reduce SM utilization for alltoall, scatter, gather, and allgather within a single (MN)NVL domain.
 * Free up SM capacity for the application to do computation at the same time.
 * To enable the feature for ncclAllGather, ncclAlltoAll, ncclGather, ncclScatter, register buffers into symmetric windows and use the NCCL_CTA_POLICY_ZERO flag in the communicator config_t.

NCCL Inspector Plugin
 * Introduces an Inspector plugin for always-on performance monitoring.
 * Produces structured JSON output with metadata, execution time, bandwidth, and optional event traces for each NCCL operation.
 * Enables integration with analysis tools such as Performance Exporter to visualize NCCL performance bottlenecks.
 * Lightweight to enable via environment variables NCCL_PROFILER_PLUGIN and NCCL_INSPECTOR_ENABLE.

CMake support (Experiemental)
 * Adds a CMake build system as an alternative to existing Makefiles.
 * Known issues: pkg.build and Device API currently do not work with CMake.
 * The known issues will be addressed in a future release.

Decreased max CTA count from 32 to 16 on Blackwell
 * SM overhead is decreased by 50% with this improvement.
 * This may cause some perf drop on Blackwell because of the reduced SM usage.
 * If the extra SM capacity is not desired, two options are available to restore to previous behavior: 1) Setting NCCL_MIN_CTAS=32 NCCL_MAX_CTAS=32 environment variables; 2) setting communicator config to over-write max CTA count to 32.
 * Based on community feedback, future versions may consider different trade-offs between performance and SM overhead.

Plugins
 * Network
   * App-aware Network plugin. NCCL passes information about communication operations to be executed on the network end point. This allows for better tuning of network end points and their use in the plugins.
   * Improve handling of physical and virtual network devices and load/unload.
   * Network plugin version 11 - add explicit context and communication ID support for per communicator init/finalize.
   * Add Multi-Request Net API. Using this will help NCCL to anticipate multiple send/recv requests and optimize for it. See maxMultiRequestSize field in ncclNetProperties_v11_t.
 * Profiler
   * Add support for API events (group, collective, and p2p) and for tracking kernel launches in the profiler plugin.
   * Add Inspector Profiler Plugin (see section above).
   * Add a hook to Google’s CoMMA profiler on github.
 * Tuner
   * Expose NCCL tuning constants at tuner initialization via ncclTunerConstants_v5_t.
   * Add NVL Domain Information API.
 * Support multiple plugin types from a single shared object.

New Parameterization and ncclConfig changes:
 * Add new option NCCL_MNNVL_CLIQUE_ID=-2 which will use rack serial number to partition the MNNVL clique. This will limit NVLink domains to GPUs within a single rack.
 * Add NCCL_NETDEVS_POLICY to control how NET devices are assigned to GPUs. The default (AUTO) is the policy used in previous versions.
 * Add NCCL_SINGLE_PROC_MEM_REG_ENABLE control variable to enable NVLS UB registration in the “one process, multiple ranks” case as opt in.
 * Move nChannelsPerNetPeer into ncclConfig. NCCL_NCHANNELS_PER_NET_PEER can override the value in ncclConfig.
 * Enable PxN over C2C by default
   * PxN over C2C will improve performance for Grace-Blackwell platforms by allowing NCCL to leverage the NIC attached to a peer GPU over NVLINK, C2C, and PCIe.
   * This behavior can be overridden by setting NCCL_PXN_C2C=0.

Other Improvements:
 * Allow FP8 support for non-reductive operations on pre sm90 devices. (See pytorch/pytorch#151594 (comment))
 * Fix NVLS+CollNet and temporarily disables COLLNET_CHAIN for >8 GPUs.
 * Only consider running interfaces for socket traffic. NCCL will not attempt to use interfaces that do not have the IFF_RUNNING bit. (#1798)
 * Modernize mutex management. Convert to std::mutex and std::lock_guard.
 * Remove sm35 and sm50 GENCODE targets which have long been deprecated and were causing issues with the latest NCCL release builds.
 * Improved NVLS/NVLSTree tuning prediction to improve algorithm and protocol selection.
 * NVLSTree Tuning Fixes. Update tuning data for H100, GB200-NV72.
 * Respond better to RoCE link flaps. Instead of reporting an “unknown event” it will now report “GID table changed”.
 * Move libvirt bridge interface to the end of possible interfaces so that they are considered last. These interfaces are usually virtual bridges to relay traffic to containers running on the host and cannot be used for traffic to a remote node and are therefore unsuitable.

Author: marksantesson

ext-net/README.md

@@ -60,36 +60,36 @@ of newer ones.
 The `nccl/` directory is populated with `net_vX.h` files extracting all relevant definitions
 from old API versions. It also provides error codes in `err.h`.
 
-# API (v10)
+# API (v11)
 
-Below is the main `ncclNet_v10` struct. Each function is explained in later sections.
+Below is the main `ncclNet_v11` struct. Each function is explained in later sections.
 
 ```
 typedef struct {
   // Name of the network (mainly for logs)
   const char* name;
   // Initialize the network.
-  ncclResult_t (*init)(ncclDebugLogger_t logFunction, ncclProfilerCallback_t profFunction);
+  ncclResult_t (*init)(void** ctx, uint64_t commId, ncclNetCommConfig_v11_t* config, ncclDebugLogger_t logFunction, ncclProfilerCallback_t profFunction);
   // Return the number of adapters.
   ncclResult_t (*devices)(int* ndev);
   // Get various device properties.
-  ncclResult_t (*getProperties)(int dev, ncclNetProperties_v10_t* props);
+  ncclResult_t (*getProperties)(int dev, ncclNetProperties_v11_t* props);
   // Create a receiving object and provide a handle to connect to it. The
   // handle can be up to NCCL_NET_HANDLE_MAXSIZE bytes and will be exchanged
   // between ranks to create a connection.
-  ncclResult_t (*listen)(int dev, void* handle, void** listenComm);
+  ncclResult_t (*listen)(void* ctx, int dev, void* handle, void** listenComm);
   // Connect to a handle and return a sending comm object for that peer.
   // This call must not block for the connection to be established, and instead
   // should return successfully with sendComm == NULL with the expectation that
   // it will be called again until sendComm != NULL.
   // If *sendDevComm points to a valid object, then NCCL is requesting device offload for this connection
-  ncclResult_t (*connect)(int dev, ncclNetCommConfig_v10_t* config, void* handle, void** sendComm, ncclNetDeviceHandle_v10_t** sendDevComm);
+  ncclResult_t (*connect)(void* ctx, int dev, void* handle, void** sendComm, ncclNetDeviceHandle_v11_t** sendDevComm);
   // Finalize connection establishment after remote peer has called connect.
   // This call must not block for the connection to be established, and instead
   // should return successfully with recvComm == NULL with the expectation that
   // it will be called again until recvComm != NULL.
   // If *recvDevComm points to a valid object, then NCCL is requesting device offload for this connection
-  ncclResult_t (*accept)(void* listenComm, void** recvComm, ncclNetDeviceHandle_v10_t** recvDevComm);
+  ncclResult_t (*accept)(void* listenComm, void** recvComm, ncclNetDeviceHandle_v11_t** recvDevComm);
   // Register/Deregister memory. Comm can be either a sendComm or a recvComm.
   // Type is either NCCL_PTR_HOST or NCCL_PTR_CUDA.
   ncclResult_t (*regMr)(void* comm, void* data, size_t size, int type, void** mhandle);
@@ -191,6 +191,12 @@ This will allow the plugin to discover network devices and make sure they are us
 `init` function does not return `ncclSuccess`, then NCCL will not use the plugin and fall back on
 internal ones.
 
+Every call to `init` returns an opaque context that the plugin uses internally to allocate resources
+and manage state. Such context is passed to other net plugin calls that create further resources,
+such as `listen` and `connect`. Every context is uniquely associated to a communicator
+using the commId. The network can also be initialized with a per communicator configuration using
+the `config` argument.
+
 To allow the plugin logs to integrate into the NCCL logs seemlessly, NCCL provides a logging
 function to `init`. This function is typically used to allow for `INFO` and `WARN` macros within
 the plugin code adding the following definitions:
@@ -282,7 +288,7 @@ side.
 `listen`
 
 To create a connection, NCCL will start by calling `listen` on the receiver side. This function
-takes a device number as input argument, and should return a local `listenComm` object, and a
+takes the opaque plugin context returned by `init` and a device number as input argument, and should return a local `listenComm` object, and a
 `handle` to pass to the other side, so that the sender side can connect to the receiver.
 
 The `handle` is a buffer of size `NCCL_NET_HANDLE_MAXSIZE` and is provided by NCCL.
@@ -304,7 +310,8 @@ the `listen` call previously. If the sender did not connect yet, `accept` should
 should return `ncclSuccess`, setting `recvComm` to `NULL`. NCCL will call `accept` again until it
 succeeds.
 
-The `connect` API takes a `ncclNetCommConfig_t`, which contains a trafficClass field.
+The `connect` API takes the opaque plugin context returned by `init`. The plugin context can reference
+the `ncclNetCommConfig_t` passed to the `init` function and containing a trafficClass field.
 This field can be used by the network plugin to specify the QoS level of the connection. By default,
 `trafficClass` is set to -1 but can be configured by the application during communicator initialization
 to select a plugin-supported QoS level.

ext-net/example/CMakeLists.txt

@@ -0,0 +1,19 @@
+set(SRC_FILES
+    ${CMAKE_CURRENT_SOURCE_DIR}/plugin.c
+)
+
+# Create shared library
+add_library(nccl-net-example SHARED ${SRC_FILES})
+
+# Set include directories
+target_include_directories(nccl-net-example PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/nccl
+)
+
+# Set output name to match Makefile
+set_target_properties(nccl-net-example PROPERTIES
+    OUTPUT_NAME "nccl-net-example"
+    PREFIX "lib"
+    POSITION_INDEPENDENT_CODE ON
+    LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/test/unit/plugins
+)

ext-net/example/nccl/net.h

@@ -22,7 +22,9 @@
 
 // Maximum number of requests per comm object
 #define NCCL_NET_MAX_REQUESTS 32
+#define NCCL_NET_MAX_DEVS_PER_NIC 4
 
+#include "net_v11.h"
 #include "net_v10.h"
 #include "net_v9.h"
 #include "net_v8.h"
@@ -33,9 +35,9 @@
 #include "net_v3.h"
 #include "net_v2.h"
 
-typedef ncclNet_v10_t ncclNet_t;
-typedef ncclNetProperties_v10_t ncclNetProperties_t;
-typedef ncclNetVDeviceProps_v10_t ncclNetVDeviceProps_t;
-typedef ncclNetCommConfig_v10_t ncclNetCommConfig_t;
+typedef ncclNet_v11_t ncclNet_t;
+typedef ncclNetProperties_v11_t ncclNetProperties_t;
+typedef ncclNetVDeviceProps_v11_t ncclNetVDeviceProps_t;
+typedef ncclNetCommConfig_v11_t ncclNetCommConfig_t;
 
 #endif // end include guard

ext-net/example/nccl/net_device.h

@@ -12,7 +12,7 @@
 
 // Arbitrary version number - A given NCCL build will only be compatible with a single device networking plugin
 // version. NCCL will check the supplied version number from net->getProperties() and compare to its internal version.
-#define NCCL_NET_DEVICE_UNPACK_VERSION 0x7  
+#define NCCL_NET_DEVICE_UNPACK_VERSION 0x7
 
 typedef enum {NCCL_NET_DEVICE_HOST=0, NCCL_NET_DEVICE_UNPACK=1} ncclNetDeviceType;
 
@@ -27,6 +27,7 @@ typedef struct {
 typedef ncclNetDeviceHandle_v7_t ncclNetDeviceHandle_v8_t;
 typedef ncclNetDeviceHandle_v8_t ncclNetDeviceHandle_v9_t;
 typedef ncclNetDeviceHandle_v9_t ncclNetDeviceHandle_v10_t;
-typedef ncclNetDeviceHandle_v10_t ncclNetDeviceHandle_t;
+typedef ncclNetDeviceHandle_v10_t ncclNetDeviceHandle_v11_t;
+typedef ncclNetDeviceHandle_v11_t ncclNetDeviceHandle_t;
 
 #endif

ext-net/example/nccl/net_v10.h

@@ -5,10 +5,9 @@
 #ifndef NET_V10_H_
 #define NET_V10_H_
 
-#define NCCL_NET_MAX_DEVS_PER_NIC_V10 4
 typedef struct {
   int ndevs;
-  int devs[NCCL_NET_MAX_DEVS_PER_NIC_V10];
+  int devs[NCCL_NET_MAX_DEVS_PER_NIC];
 } ncclNetVDeviceProps_v10_t;
 
 

ext-net/example/nccl/net_v11.h

@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 2017-2022, NVIDIA CORPORATION. All rights reserved.
+ */
+
+#ifndef NET_V11_H_
+#define NET_V11_H_
+
+typedef struct {
+  int ndevs;
+  int devs[NCCL_NET_MAX_DEVS_PER_NIC];
+} ncclNetVDeviceProps_v11_t;
+
+#define NCCL_NET_TRAFFIC_CLASS_UNDEF -1
+
+typedef struct {
+  // Plugin-specific TC value
+  int trafficClass;
+} ncclNetCommConfig_v11_t;
+
+
+typedef struct {
+  char* name;                      // Used mostly for logging.
+  char* pciPath;                   // Path to the PCI device in /sys.
+  uint64_t guid;                   // Unique identifier for the NIC chip. Important for
+                                   // cards with multiple PCI functions (Physical or virtual).
+  int ptrSupport;                  // [NCCL_PTR_HOST|NCCL_PTR_CUDA|NCCL_PTR_DMABUF]
+  int regIsGlobal;                 // regMr is not tied to a particular comm
+  int forceFlush;                  // Force a flush on receives
+  int speed;                       // Port speed in Mbps.
+  int port;                        // Port number.
+  float latency;                   // Network latency
+  int maxComms;                    // Maximum number of comms we can create
+  int maxRecvs;                    // Maximum number of grouped receives.
+  ncclNetDeviceType netDeviceType; // Network offload type
+  int netDeviceVersion;            // Version number for network offload
+  ncclNetVDeviceProps_v11_t vProps;
+  size_t maxP2pBytes;              // Max transfer size for point-to-point operations
+  size_t maxCollBytes;             // Max transfer size for collective operations
+  int maxMultiRequestSize;         // Maximum number of requests supported in a single multi-request.
+} ncclNetProperties_v11_t;
+
+typedef struct {
+  int32_t maxConcurrentPeers;
+  int32_t minConcurrentPeers;
+  int32_t maxFlowsPerPeer;
+  int32_t minFlowsPerPeer;
+} ncclNetCommAttr_v11_t;
+
+typedef struct {
+  ncclNetCommAttr_v11_t sendCommAttr;
+  ncclNetCommAttr_v11_t recvCommAttr;
+  uint32_t op;
+  uint32_t algo;
+  uint32_t proto;
+} ncclNetAttr_v11_t;
+
+typedef struct {
+  // Name of the network (mainly for logs)
+  const char* name;
+  // Initialize the network.
+  ncclResult_t (*init)(void** ctx, uint64_t commId, ncclNetCommConfig_v11_t* config, ncclDebugLogger_t logFunction, ncclProfilerCallback_t profFunction);
+  // Return the number of adapters.
+  ncclResult_t (*devices)(int* ndev);
+  // Get various device properties.
+  ncclResult_t (*getProperties)(int dev, ncclNetProperties_v11_t* props);
+  // Create a receiving object and provide a handle to connect to it. The
+  // handle can be up to NCCL_NET_HANDLE_MAXSIZE bytes and will be exchanged
+  // between ranks to create a connection.
+  ncclResult_t (*listen)(void* ctx, int dev, void* handle, void** listenComm);
+  // Connect to a handle and return a sending comm object for that peer.
+  // This call must not block for the connection to be established, and instead
+  // should return successfully with sendComm == NULL with the expectation that
+  // it will be called again until sendComm != NULL.
+  // If *sendDevComm points to a valid object, then NCCL is requesting device offload for this connection
+  ncclResult_t (*connect)(void* ctx, int dev, void* handle, void** sendComm, ncclNetDeviceHandle_v11_t** sendDevComm);
+  // Finalize connection establishment after remote peer has called connect.
+  // This call must not block for the connection to be established, and instead
+  // should return successfully with recvComm == NULL with the expectation that
+  // it will be called again until recvComm != NULL.
+  // If *recvDevComm points to a valid object, then NCCL is requesting device offload for this connection
+  ncclResult_t (*accept)(void* listenComm, void** recvComm, ncclNetDeviceHandle_v11_t** recvDevComm);
+  // Register/Deregister memory. Comm can be either a sendComm or a recvComm.
+  // Type is either NCCL_PTR_HOST or NCCL_PTR_CUDA.
+  ncclResult_t (*regMr)(void* comm, void* data, size_t size, int type, void** mhandle);
+  /* DMA-BUF support */
+  ncclResult_t (*regMrDmaBuf)(void* comm, void* data, size_t size, int type, uint64_t offset, int fd, void** mhandle);
+  ncclResult_t (*deregMr)(void* comm, void* mhandle);
+  // Asynchronous send to a peer.
+  // May return request == NULL if the call cannot be performed (or would block)
+  ncclResult_t (*isend)(void* sendComm, void* data, size_t size, int tag, void* mhandle, void* phandle, void** request);
+  // Asynchronous recv from a peer.
+  // May return request == NULL if the call cannot be performed (or would block)
+  ncclResult_t (*irecv)(void* recvComm, int n, void** data, size_t* sizes, int* tags, void** mhandles, void** phandles, void** request);
+  // Perform a flush/fence to make sure all data received with NCCL_PTR_CUDA is
+  // visible to the GPU
+  ncclResult_t (*iflush)(void* recvComm, int n, void** data, int* sizes, void** mhandles, void** request);
+  // Test whether a request is complete. If size is not NULL, it returns the
+  // number of bytes sent/received.
+  ncclResult_t (*test)(void* request, int* done, int* sizes);
+  // Close and free send/recv comm objects
+  ncclResult_t (*closeSend)(void* sendComm);
+  ncclResult_t (*closeRecv)(void* recvComm);
+  ncclResult_t (*closeListen)(void* listenComm);
+
+  // Copy the given mhandle to a dptr in a format usable by this plugin's device code
+  ncclResult_t (*getDeviceMr)(void* comm, void* mhandle, void** dptr_mhandle);
+
+  // Notify the plugin that a recv has completed by the device
+  ncclResult_t (*irecvConsumed)(void* recvComm, int n, void* request);
+
+  // Virtual NIC APIs. makeVDevice will create a virtual NIC given the specified properties, and tell the caller
+  // what index this new vNIC exists at
+  ncclResult_t (*makeVDevice)(int* d, ncclNetVDeviceProps_v11_t* props);
+  // Finalize the network.
+  ncclResult_t (*finalize)(void* ctx);
+
+  ncclResult_t (*setNetAttr)(void* ctx, ncclNetAttr_v11_t* netAttr);
+} ncclNet_v11_t;
+
+#endif // end include guard

ext-net/example/nccl/net_v9.h

@@ -5,10 +5,9 @@
 #ifndef NET_V9_H_
 #define NET_V9_H_
 
-#define NCCL_NET_MAX_DEVS_PER_NIC_V9 4
 typedef struct {
   int ndevs;
-  int devs[NCCL_NET_MAX_DEVS_PER_NIC_V9];
+  int devs[NCCL_NET_MAX_DEVS_PER_NIC];
 } ncclNetVDeviceProps_v9_t;
 
 typedef struct {