# Changelog for RCCL

Full documentation for RCCL is available at [https://rccl.readthedocs.io](https://rccl.readthedocs.io)

## RCCL 2.30.4 for ROCm 7.14.0

### Added
* Compatibility with NCCL 2.30.4.
* Compatibility with NCCL 2.29.7.
* Compatibility with NCCL 2.28.9.
* Added proxytrace profiler plugin and core proxy-diagnostics hooks (`RCCL_PROXYTRACE`).
* Added `ncclBarrierSession` LSA validation for barrier sessions.
* Added symmetric-memory ReduceScatter kernel (`RailA2A_LsaLD`) on gfx942/gfx950.
* Added bias (accumulation) AllReduce on gfx1250 (MI450).
* Added optimized scale-up ReduceScatter, AllGather, and AllToAll kernels.
* Added ROCProfiler-SDK coverage for `ncclCommGrow` and `ncclCommGetUniqueId`.
* P2P batching auto-enabled for gfx950 in combination with non-AINIC NICs.
* Display HIP/ROCm runtime versions in `NCCL_DEBUG` output.
* Detect ROCm version via core symlink for multi-architecture installs.
* Skip DDA IPC initialization for directMode and MNNVL topologies.
* Load versioned `libamd_smi` SONAME instead of an unversioned symlink.
* Added Pythonic API bindings under `bindings/nccl4py/` (RCCL fork of NVIDIA `nccl4py` v0.2.0). Provides Python access to RCCL collectives via Cython bindings, an on-disk `cuda.core` HIP shim for ROCm hosts without `cuda-bindings` / `cuda-core`, and RCCL-only collective wrappers (`ncclAllReduceWithBias`, `ncclAllToAllv`).
* Added RCCL examples to the repository.
* Added `RCCL host API` pull-in from NCCL 2.30.

### Changed
* Enabled WarpSpeed auto mode for grow communicators.
* Refactored AllGather algorithm selection; hierarchical AllGather now enabled by default for multi-node.
* Swapped legacy `net_ib` with the `net_ib` implementation from NCCL 2.29.
* Skip per-warp channel LDS copy when `warpComm` is disabled.
* Hardened proxy RPC setup against malformed peer input.
* The bootstrap AllGather now uses the bidirectional ring (N/2 steps) by default on the socket OOB path. `NCCL_BOOTSTRAP_BIDIR_ALLGATHER` now defaults to `1`; set it to `0` to fall back to the unidirectional ring. The net OOB path (`NCCL_OOB_NET_ENABLE`) and its bidirectional variant (`NCCL_BOOTSTRAP_BIDIR_NET`) remain off by default.
* `NCCL_PXN_C2C` is kept default-off (`0`); upstream NCCL defaults it to `1` since 2.28. The C2C PXN routing path is NVIDIA-specific and is not currently applicable on AMD hardware.

### Removed
* Removed NPKit profiling support (build option ``ENABLE_NPKIT``, headers, device and proxy instrumentation, install script flag ``--npkit-enable``, and related documentation and tooling). Use the profiler plugin API for profiling instead.
* Removed kernel COLLTRACE support, including the `COLLTRACE` build option, device-side collective trace buffers, debug kernel variants, and related install/CI wiring. The host latency profiler is unchanged.
* Removed legacy `ENABLE_PROFILING` device profiling support and the `PROFILE` build option. Use the profiler plugin API instead.

### Optimized
* Tuned symmetric memory kernels.
* Parallelized communicator destruction across child processes to reduce teardown latency.

### Resolved issues
* Fixed `ncclCommGrow` channel-count divergence causing incorrect collective routing.
* Fixed `ncclCommGrow` hang when growing to an 8-rank single-node communicator.
* Fixed symmetric LDS under-reservation in legacy (non-device-linker) builds.
* Fixed LL128 protocol correctness for gfx1250 (MI450).
* Fixed XGMI topology mapping for multi-system (NPS) nodes.
* Fixed gfx950 collective hang caused by a tuner race condition.
* Fixed `net_ib_cast`: gate CTS offload path on per-connection state.
* Fixed `net_ib`: avoid flagging a non-fatal Isend CTS no-match as a fatal error.
* Fixed acquire-tail polling for gfx950 P2P host staging.
* Fixed LDS overflow in device-linker builds.
* Fixed symmetric memory correctness issues.
* Fixed `ncclCommFree` to free symmetric window objects automatically (NCCL 2.29.7 defect).
* Fixed DDA IPC initialization skip on architectures that do not run DDA.
* Fixed static build (`BUILD_SHARED_LIBS=OFF`) failing with `install(EXPORT "rccl-targets" ...)` error when `fmt` is fetched via `FetchContent`. The `fmt-header-only` target is now scoped to the build interface and excluded from RCCL's exported usage requirements.
* Fixed proxy channel staging buffers ignoring the new GDR mode selection on HIP < 7.12 builds. The legacy `#else` branch in `sendProxyConnect` / `recvProxyConnect` now honors `resources->useDmaBuf`, so peermem-equipped hosts on older HIP no longer fall through to `hsa_amd_portable_export_dmabuf` when peermem was selected in `*ProxySetup`. Workaround for affected RCCL builds: `NCCL_DMABUF_ENABLE=0`.
* Fixed RCCL initialization failing (`Failed to find ROCm runtime library`) on runtime-only ROCm trees that ship no unversioned `libhsa-runtime64.so` developer symlink (e.g. TheRock multi-arch pip-wheel `/opt/rocm-less` deployments). RCCL no longer `dlopen`s the HSA runtime by name; instead it directly links `hsa-runtime64::hsa-runtime64` (already a hard transitive dependency via the HIP runtime) and binds `hsa_init`, `hsa_system_get_info`, `hsa_status_string`, and `hsa_amd_portable_export_dmabuf` to those symbols. The linker records `DT_NEEDED libhsa-runtime64.so.1` and resolves it through librccl's existing RPATH, removing the SONAME version-string fragility and load-scope (`RTLD_LOCAL`) issues. The `RCCL_ROCR_PATH` override is no longer needed and has been removed.
* Retagged the RCCL-only `COLLTRACE` destroy-time log lines from `NCCL_INIT` to `NCCL_DESTROY` and documented the `DESTROY` `NCCL_DEBUG_SUBSYS` subsystem. The NCCL 2.30.3 sync added `NCCL_DESTROY` and retagged the shared comm-destroy/plugin-unload log lines, but missed these RCCL-specific lines since `COLLTRACE` has no upstream equivalent; they are now excluded from `NCCL_DEBUG=INFO` output by default, consistent with the other destroy-time lines.

### Known issues
* On gfx90a (MI210/MI250/MI250X) with ROCm 7.13 or later, per-launch scratch-memory reclaim in the runtime degrades RCCL performance. Set `HSA_NO_SCRATCH_RECLAIM=1` to restore performance.
* Elastic-buffer support for GIN (multi-segment symmetric memory windows backed by a mix of device and CPU/`HOST_NUMA` memory, exposed through `NCCL_ELASTIC_BUFFER_REGISTER` and `NCCL_SYM_REUSE_SYSMEM_HANDLES`) was newly synced from upstream and compiles on ROCm, but is unverified on AMD hardware.

## RCCL 2.28.3 for ROCm 7.13

### Added
* Added CAST network transport (`ncclNetCast` / `net_ib_cast`) for AMD AINIC hardware.
* Added built-in CSV tuner for runtime algorithm/protocol/channel selection without rebuilds.
* Added multi-node hierarchical AllGather algorithm for MI350. Hierarchical AllGather is enabled by default for 8 or more nodes. The message size threshold is 64MB on 8 nodes and 128MB for more than 8 nodes. Set `RCCL_HIERARCHICAL_ALLGATHER=0` to disable.
* Initial support for symmetric memory kernels on gfx942 and gfx950.
* Added `RCCL_IB_SPLIT_DATA_THRESHOLD` to split payload across multiple QPs/NICs in `ncclIbMultiSend`.
* Round-robin single-QP payload and fifo-head-based QP selection in `ncclIbMultiSend`.
* Added User Buffer and Graph Registration (`NCCL_NVLS_ENABLE` / CUMEM) gated on Linux kernel version.
* Added runtime QP tracking with atomic counters in `net_ib` and `net_ib_cast`.
* Enable Copy Engine (CE) collectives support in RCCL.
* Added gfx1250 (MI450) GPU target support in RCCL and RCCL-Tests.
* Strix-Halo (gfx1151) tuning support.
* Add `amd-smi` wrapper functions for projected scale-up support, fabric capability dumping, and MNNVL fabric checks.
* Added `RCCL_IB_P2P_DISABLE_CTS` to disable CTS offload for P2P connections on AINIC. Defaults to 1 (disabled). When `RCCL_CTS_OFFLOAD_ENABLED=1` is explicitly set, it overrides this flag and forces CTS on all connections including P2P.
* Merged `RCCL_CTS_INLINE_DATA` into `RCCL_CTS_OFFLOAD_ENABLED`. CTS offload and CTS inline data are now controlled by a single tri-state variable: `-1` (default, auto-enable on AINIC), `0` (force disable), `1` (force enable for all connections).

### Changed
* Removed MSCCL and MSCCL++ collective integration; legacy `mscclLoadAlgo`, `mscclRunAlgo`, and `mscclUnloadAlgo` APIs remain as no-ops for link compatibility.
* Removed roc-obj tools and perl build dependency.
* Disable P2P batching by default on MI350.
* Disable AMD-SMI (`amdsmi_init`) by default due to a concurrency issue in `amdsmi_init`; enable explicitly for ROCm 7.0 and above when the issue is addressed.
* `RCCL_ENABLE_CONTEXT_TRACKING` replaced by `NCCL_LAUNCH_ORDER_IMPLICIT` for controlling launch-order tracking.
* Moved tuning log messages from `NCCL_INIT` to the `NCCL_TUNING` debug subsystem.
* Gate multi-node Direct AllGather on PXN enablement.
* Use 256 threads per block on gfx950 (increased from 512).
* Set algorithm to Ring for Navi4x (gfx1100/gfx1101) AllReduce.
* Proxy busy-spin loop replaced with architecture-specific pause instruction on GDA-eligible topologies.
* RCCL adds a NCCL CMake alias shim layer for CMake-based build compatibility.
* CTS offload is now controlled per-connection rather than globally, allowing P2P connections to fall back to standard RDMA writes while non-P2P traffic continues to use CTS.

### Resolved Issues
* Fixed `netOverride` being skipped when rail-optimized trees are enabled (restores desired NIC mapping for targeted 4-NIC systems).
* Fixed RCCL Inspector plugin teardown segfault/hang and collective-count correctness.
* Fixed `ncclGroupSimulateEnd` planner state leak and resource cleanup.
* Fixed validation errors with `all_reduce_bias` kernel on gfx950.
* WarpSpeed now errors out with a warning when the requested channel count exceeds the maximum supported.
* Fixed `--generate-sym-kernels` option when used with the default `--device-linker`.
* Fixed `CUCHECK` and `CUCHECKGOTO` macros to clear the HIP error state before returning.
* Fixed `amd-smi`/`rocm-smi` enum mismatch.
* Fixed CTS-offload corner cases in `net_ib_rocm` and `net_ib_cast` (including mutual dependency enforcement with NIC fusion).
* Fixed IPC registration incorrect `#ifdef` guard that disabled registration.
* Fixed symmetric kernels validation errors on gfx942 and gfx950.

## RCCL 2.28.3 for ROCm 7.12

### Added
* Added gfx1151 (Strix-Halo) GPU target support.
* Added AMD AINIC support within the RCCL default internal network plugin.
* Added `RCCL_P2P_SHIFT_SIZE` environment variable for advanced tuning of P2P channel and part mapping.
* Added Direct Reduce Scatter implementation for improved multi-node performance.
* Added WarpSpeed support for single-node AllGather and ReduceScatter.
* Added virtual device enablement support (minimal changes for virtual GPU topology).
* Added Navi4 (gfx1100) LL protocol enablement and tuning.
* Added add-smi wrapper for firmware version queries (switched from rocm-smi to amd-smi).

### Changed
* Changed GPU Direct RDMA mode selection logic to prefer peermem over DMAbuf by default. `NCCL_DMABUF_ENABLE` now defaults to 1 (previously 0). When both peermem and DMAbuf are available, RCCL will use peermem. If peermem is unavailable, RCCL will automatically fall back to DMAbuf (if available and enabled). Setting `RCCL_FORCE_ENABLE_DMABUF=1` forces DMAbuf usage exclusively, skipping peermem even if available, and disables GPU Direct RDMA if DMAbuf is unavailable.
* Remove P2P batching node-count cap; P2P batching now applies for all node counts (previously capped at 32 nodes).
* Halved default CU usage for gfx950 single-node all-reduce for better resource efficiency.
* Set default maximum channels to 48 for gfx950 multi-node collectives.
* Set default maximum channels to 48 for MI350 multi-node collectives.
* WarpSpeed auto-mode handling improved; WarpSpeed enabled for MI350 single-node.
* `NCCL_LAUNCH_ORDER_IMPLICIT` replaces `RCCL_ENABLE_CONTEXT_TRACKING` for controlling implicit launch ordering.
* Disable Direct Reduce Scatter automatically when PXN is disabled.
* Tuning: constant values used for CorrectionFactor tables for improved consistency.
* DMABUF disabled configurations now correctly respected in `rocm_net_ib`.

### Resolved Issues
* Fixed shutdown ordering race condition and use-after-free crash in proxy cleanup.
* Fixed DMABUF support check failure (SWDEV-579889 / ROCM-2855).
* Fixed `qpIndex` selection in `ncclIbIrecv` for AINIC mode.
* Fixed per-device UD map indexing for NIC fusion configurations.
* Fixed potential segfaults from `malloc` failure paths.
* Fixed bfloat16 reduce kernel bug for ROCm >= 6.0.
* Fixed memory leak in `ncclCommInitRankFunc`.
* Fixed memory leaks (ROCM-1721, ROCM-1722).

### Known issues
* The upstream one-sided RMA subsystem (`src/rma`) was newly synced and uses RCCL's direct-HIP batch memory-operation path (`hipStreamBatchMemOp`, in place of the upstream CUDA `ncclCuStreamBatchMemOp` driver wrapper which is not built on ROCm). It is unverified at scale on ROCm.
* The upstream Copy-Engine (CE) collective redesign (device-side sequence-number buffer driven by `cuStreamWriteValue32`/`cudaMemcpyAsync`) is not adopted. RCCL retains its existing self-consistent HIP Copy-Engine implementation, which is structurally incompatible with the new upstream path.
* The Copy-Engine profiler path (`ncclProfiler_v6`) is not enabled; RCCL remains on `ncclProfiler_v5`. The profiler plugin needs to be verified on ROCm.
* GIN GDAKI host support now uses the shared InfiniBand context (`ibv_context`/`ibv_pd`) rather than opening its own device. The GDAKI path is DOCA/Mellanox-specific and is unverified on AMD NICs.
* The RCCL InfiniBand GIN proxy backend was ported to the reworked NCCL 2.30.3 `ncclGin_v13_t` interface (opaque per-communicator context with mandatory `createContext`/`destroyContext`), but does not implement GIN GET or FLUSH (`iget`/`iflush` are left unset); the GIN host proxy reports an unsupported-op error if a device kernel requests one.
* Elastic-buffer support for GIN (multi-segment symmetric memory windows backed by a mix of device and CPU/`HOST_NUMA` memory, exposed through `NCCL_ELASTIC_BUFFER_REGISTER` and `NCCL_SYM_REUSE_SYSMEM_HANDLES`) was newly synced from upstream and compiles on ROCm, but is unverified on AMD hardware.

## RCCL 2.28.3 for ROCm 7.11

### Known issues
* AllToAllv and AllToAll for a single GPU is hanging.
* AllGather regression for small message sizes (less than 1 MB) due to the Direct algorithm.
* ROCTx feature needs to be verified.
* Profiler plugin needs to be verified.

### Added
* Compatibility with NCCL 2.28.3.
* Added `ncclAllReduceWithBias` API for fused all-reduce with elementwise accumulation-bias operations.
* Added collective latency profiler tool (`--latency-profiler` in `install.sh`) for per-collective timing analysis.
* Added dynamic pipelining for reduction collectives via the Simple protocol to improve single-node performance.
* Added `unroll=2` device-code variant for gfx950 multi-node collectives.
* Enable LL128 protocol for gfx942 with 4-NIC configurations using a unified tuning table.
* Added reduce/broadcast algorithm and protocol selection tuning table for multi-node gfx940.
* Pass `NET_OPTIONAL_RECV_COMPLETION` hint to the network plugin to enable potential network-side optimizations.
* Expose symbols for RCCL algorithm, protocol, and channels selection functions (`rcclOverrideAlgorithm`, `rcclOverrideProtocol`).
* Added rail-optimized tree topology support for MI3XX nodes with 4 NICs.
* Added single-node AllGather and ReduceScatter performance optimizations.
* Enable GDRCopy option for gfx950.
* Enable single-node one-slice optimization for gfx950 and MI300A.
* Added environment variable to cap the number of QPs created for send/recv collectives.
* Added support for additional paths when loading the RCCL DMABUF kernel configuration file.
* Added `ncclCommDump` API for communicator state inspection.
* Added rocSHMEM GDA alltoall integration (GDA-accelerated alltoall via rocSHMEM).

### Changed
* PIX and PXB are now treated as equivalent GDR distances for more consistent topology detection.
* Optimized AllToAll for 64 or more GPUs on gfx942.
* Optimize `threadfence` for the LL64 protocol on the sender side.
* Disable `__threadfence` on the sender side of the Simple protocol when it is not needed for correctness.
* Use rocm-smi API instead of CLI invocation for firmware version querying.
* Adjusted gfx950 thread-block size to improve LL64 and Simple protocol performance for AllReduce, AllGather, and ReduceScatter.
* `__threadfence` bypass on the multinode gfx950 sender side is now the default.
* Updated multi-node LL/LL128 tuning for gfx950 to improve large-message bandwidth.
* Disabled graph mode memory registration and user buffer registration as unsupported features on current hardware.
* Updated Direct AllGather threshold for single-node and multi-node cases.
* Experimental support for traffic shaping using warp specialization (also known as WarpSpeed) is now available for the Ring algorithm.
* Enabling WarpSpeed in auto mode using RCCL_WARP_SPEED_AUTO optimizes performance and reduces the CU count by 50% on a single node for AllReduce, AllGather from 64MB, and ReduceScatter from 256MB.
* The following configuration knobs control WarpSpeed behavior for debugging purposes: `RCCL_WARP_SPEED_ENABLE`, `RCCL_UNROLL_FACTOR`, `RCCL_WARP_SPEED_CU_COUNT`, and `RCCL_THREADS_PER_BLOCK`. Note that the effective unroll factor is calculated as 2 raised to the value of `RCCL_UNROLL_FACTOR`.

### Resolved Issues
* Fixed missing memory fence in the LL protocol for gfx950, which caused collective hangs.
* Fixed segmentation fault in the external profiler plugin on communicator teardown.
* Fixed LL128 protocol selection to respect the user's explicit protocol override setting.
* Fixed `rcclNetP2pPolicy` returning incorrect policy for multi-NIC configurations.
* Fixed missing proxy-counter updates in the proxy loop leading to stalled counters.
* Fixed P2P batching hang when using batch operations.
* Fixed P2P self-copy for batched operations to prevent hangs when communicator size exceeds 32 nodes.
* Fixed WarpSpeed auto mode selection bug.

## RCCL 2.27.7 for ROCm 7.2.0

### Changed
* RCCL error messages have been made more verbose in several cases. RCCL now prints out fatal error messages by default. Fatal error messages can be suppressed by setting `NCCL_DEBUG=NONE`.
* Disabled `reduceCopyPacks` pipelining for `gfx950`.

### Known issues
* AllToAllv/AlltoAll for single GPU is hanging.

## RCCL 2.27.7 for ROCm 7.1.1

### Changed
* Enabling P2P batching with `RCCL_P2P_BATCH_ENABLE=1` is only applicable up to 32 nodes.

### Resolved Issues

* Fixed crash when using the librccl-profiler plugin with the all-to-all collective after the 2.27 update.

## RCCL 2.27.7 for ROCm 7.1.0

### Added
* Added `RCCL_IB_QPS_PER_P2P` to set the number of QPs per connection for P2P operations. When set (≥1), P2P operations (Send/Recv) use `RCCL_IB_QPS_PER_P2P`, while other collective operations continue to use `NCCL_IB_QPS_PER_CONNECTION`. When not set, `NCCL_IB_QPS_PER_CONNECTION` applies to all operations.
* Added `RCCL_FORCE_ENABLE_DMABUF` as a debugging feature if the user wants to explicitly enable DMABUF and forego system/kernel checks.
* Added `RCCL_P2P_BATCH_THRESHOLD` to set the message size limit for batching P2P operations. This mainly affects small message performance for alltoall at a large scale but also applies to alltoallv.
* Added `RCCL_P2P_BATCH_ENABLE` to enable batching P2P operations to receive performance gains for smaller messages up to 4MB for alltoall when the workload requires it. This is to avoid performance dips for larger messages.
* Added `RCCL_CHANNEL_TUNING_ENABLE` to enable channel tuning that overrides RCCL's internal adjustments based on threadThreshold.


### Changed

* The MSCCL++ feature is now disabled by default. The `--disable-mscclpp` build flag is replaced with `--enable-mscclpp` in the `rccl/install.sh` script.
* Compatibility with NCCL 2.27.7.

### Optimized
* Enabled and optimized batched P2P operations to improve small message performance for AllToAll and AllGather.
* Optimized channel count selection to improve efficiency for small to medium message sizes in ReduceScatter.
* Changed code inlining to improve latency for small message sizes for AllReduce, AllGather, and ReduceScatter.

### Known issues
* Symmetric memory kernels are currently disabled due to ongoing CUMEM enablement work.
* When running this version of RCCL using ROCm versions earlier than 6.4.0, the user must set the environment flag `HSA_NO_SCRATCH_RECLAIM=1`.

## RCCL 2.26.6 for ROCm 7.0.0

### Resolved issues

* Resolved an issue when using more than 64 channels when multiple collectives are used in the same `ncclGroup()` call.
* Fixed unit test failures in tests ending with `ManagedMem` and `ManagedMemGraph` suffixes.
* Suboptimal algorithmic switching point for AllReduce on MI300x.
* Fixed the known issue "When splitting a communicator using `ncclCommSplit` in some GPU configurations, MSCCL initialization can cause a segmentation fault." with a design change to use `comm` instead of `rank` for `mscclStatus`. The Global map for `comm` to `mscclStatus` is still not thread safe but should be explicitly handled by mutexes for read writes. This is tested for correctness, but there is a plan to use a thread-safe map data structure in upcoming changes.
* Fixed broken functionality within the LL protocol on gfx950 by disabling inlining of LLGenericOp kernels.

### Added

* Added new GPU target `gfx950`.
* Added support for `unroll=1` in device-code generation to improve performance,
* Set a default of 112 channels for a single node with `8 * gfx950`,
* Enabled LL128 protocol on `gfx950`.
* Added MSCCL support for AllGather multinode gfx942/gfx950 (i.e., 16 and 32 GPUs). To enable, set the environment variable `RCCL_MSCCL_FORCE_ENABLE=1`. Max message size for MSCCL AllGather usage is `12292 * sizeof(datatype) * nGPUs`.
* Thread thresholds for LL/LL128 are selected in Tuning Models for the MI300X. This impacts the number of channels used for AG and RS. Channel tuning model is bypassed if `NCCL_THREAD_THRESHOLDS`, `NCCL_MIN_NCHANNELS', or 'NCCL_MAX_NCHANNELS` are set.
* Multi-node tuning for AllGather, AllReduce, and ReduceScatter that leverages LL/LL64/LL128 protocol to use nontemporal vector load/store for tunable message size ranges.
* LL/LL128 usage ranges for AR, AG, and RS are part of the tuning models, which enable architecture-specific tuning in conjunction with the existing Rome Models scheme in RCCL.
* Two new APIs are exposed as part of an initiative to separate RCCL code. These APIs are `rcclGetAlgoInfo` and `rcclFuncMaxSendRecvCount`. However, user-level invocation requires that RCCL be built with `RCCL_EXPOSE_STATIC` enabled.
* Enabled double-buffering in `reduceCopyPacks` to trigger pipelining, especially to overlap `bf16` arithmetic and bridge the gap between `fp32` performance and `bf16` for both `gfx942` and `gfx950`. Pipelining has been made tunable via `rcclSetPipelining`, similar to algorithms/protocols so that regression is avoided in certain message sizes.
* Added a direct allgather algorithm. This is enabled by default for multi-node if there are 16 nodes or fewer. The message size threshold is 4MB.
* Added `RCCL_OVERRIDE_PROTO` and `RCCL_OVERRIDE_ALGO` to allow direct replacement of protocol and algorithm choices. Unlike `NCCL_PROTO` and `NCCL_ALGO`, which re-run the model across enabled combinations and may not guarantee the intended override, these new options enforce the specified selections explicitly.

### Changed

* Compatibility with NCCL 2.23.4.
* Compatibility with NCCL 2.24.3.
* Compatibility with NCCL 2.25.1.
* Compatibility with NCCL 2.26.6.

### Optimized
* Improved the performance of the `FP8` Sum operation by upcasting to `FP16`.

### Known Issues
* When running this version of RCCL using ROCm versions earlier than 6.4.0, the user must set the environment flag `HSA_NO_SCRATCH_RECLAIM=1`.

## RCCL 2.22.3 for ROCm 6.4.2

### Added

* Added support for the LL128 protocol on gfx942.

## RCCL 2.22.3 for ROCm 6.4.1

### Resolved issues

* Fixed the accuracy issue for MSCCLPP `allreduce7` kernel in graph mode.
* Fixed IntraNet performance.
* Fixed an issue where, in rare circumstances, the application could stop responding due to a proxy thread synchronization issue.

### Known issues

* When splitting a communicator using `ncclCommSplit` in some GPU configurations, MSCCL initialization can cause a segmentation fault.
  The recommended workaround is to disable MSCCL with `export RCCL_MSCCL_ENABLE=0`.
* Within the RCCL-UnitTests test suite, failures occur in tests ending with the `ManagedMem` and `ManagedMemGraph` suffixes. These failures only affect the test results and do not affect the RCCL component itself. This issue will be resolved in the next major release.

## RCCL 2.22.3 for ROCm 6.4.0

### Added

* `RCCL_SOCKET_REUSEADDR` and `RCCL_SOCKET_LINGER` environment parameters.
* Setting `NCCL_DEBUG=TRACE NCCL_DEBUG_SUBSYS=VERBS` will generate traces for fifo and data `ibv_post_sends`.
* Added `--log-trace` flag to enable traces through the install.sh script (e.g. `./install.sh --log-trace`).

### Changed

* Compatibility with NCCL 2.22.3
* Added support for the rail-optimized tree algorithm for the MI300 series. This feature requires the use of all eight GPUs within
  each node. It limits NIC traffic to use only GPUs of the same index across nodes and should not impact performance
  on non-rail-optimized network topologies. The original method of building trees can be enabled by setting the
  environment variable `RCCL_DISABLE_RAIL_TREES=1`.
* Additional debug information about how the trees are built can be logged to the GRAPH logging subsys by setting
  `RCCL_OUTPUT_TREES=1`.
* Added documentation about the NPS4 and CPX partition modes performance benefits on the MI300X.

## RCCL 2.21.5 for ROCm 6.3.1

### Added

### Changed

* Enhanced user documentation

### Resolved issues

* Corrected user help strings in `install.sh`

## RCCL 2.21.5 for ROCm 6.3.0

### Added

* MSCCL++ integration for AllReduce and AllGather on gfx942
* Performance collection to rccl_replayer
* Tuner Plugin example for MI300
* Tuning table for large number of nodes
* Support for amdclang++
* Allow NIC ID remapping using `NCCL_RINGS_REMAP` environment variable

### Changed

* Compatibility with NCCL 2.21.5
* Increased channel count for MI300X multi-node
* Enabled MSCCL for single-process multi-threaded contexts
* Enabled gfx12
* Enabled CPX mode for MI300X
* Enabled tracing with rocprof
* Improved version reporting
* Enabled GDRDMA for Linux kernel 6.4.0+

### Resolved issues

* Fixed model matching with PXN enable

## RCCL 2.20.5 for ROCm 6.2.1
### Fixed
- GDR support flag now set with DMABUF
### Known issues
- On systems running Linux kernel 6.8.0, such as Ubuntu 24.04, Direct Memory Access (DMA) transfers between the GPU and NIC are disabled and impacts multi-node RCCL performance.
  - This issue was reproduced with RCCL 2.20.5 (ROCm 6.2.0 and 6.2.1) on systems with Broadcom Thor-2 NICs and affects other systems with RoCE networks using Linux 6.8.0 or newer.
  - Older RCCL versions are also impacted.
  - This issue will be addressed in a future ROCm release.

## RCCL 2.20.5 for ROCm 6.2.0
### Changed
- Compatibility with NCCL 2.20.5
- Compatibility with NCCL 2.19.4
- Performance tuning for some collective operations on MI300
- Enabled NVTX code in RCCL
- Replaced rccl_bfloat16 with hip_bfloat16
- NPKit updates:
  - Removed warm-up iteration removal by default, need to opt in now
  - Doubled the size of buffers to accommodate for more channels
- Modified rings to be rail-optimized topology friendly
- Replaced ROCmSoftwarePlatform links with ROCm links
### Added
- Support for fp8 and rccl_bfloat8
- Support for using HIP contiguous memory
- Implemented ROC-TX for host-side profiling
- Enabled static build
- Added new rome model
- Added fp16 and fp8 cases to unit tests
- New unit test for main kernel stack size
- New -n option for topo_expl to override # of nodes
- Improved debug messages of memory allocations
### Fixed
- Bug when configuring RCCL for only LL128 protocol
- Scratch memory allocation after API change for MSCCL

## RCCL 2.18.6 for ROCm 6.1.0
### Changed
- Compatibility with NCCL 2.18.6

## RCCL 2.18.3 for ROCm 6.0.0
### Changed
- Compatibility with NCCL 2.18.3

## RCCL 2.17.1-1 for ROCm 5.7.0
### Changed
- Compatibility with NCCL 2.17.1-1
- Performance tuning for some collective operations
### Added
- Minor improvements to MSCCL codepath
- NCCL_NCHANNELS_PER_PEER support
- Improved compilation performance
- Support for gfx94x
### Fixed
- Potential race-condition during ncclSocketClose()

## RCCL 2.16.2 for ROCm 5.6.0
### Changed
- Compatibility with NCCL 2.16.2
### Fixed
- Remove workaround and use indirect function call

## RCCL 2.15.5 for ROCm 5.5.0
### Changed
- Compatibility with NCCL 2.15.5
- Unit test executable renamed to rccl-UnitTests
### Added
- HW-topology aware binary tree implementation
- Experimental support for MSCCL
- New unit tests for hipGraph support
- NPKit integration
### Fixed
- rocm-smi ID conversion
- Support for HIP_VISIBLE_DEVICES for unit tests
- Support for p2p transfers to non (HIP) visible devices
### Removed
- Removed TransferBench from tools.  Exists in standalone repo: https://github.com/ROCm/TransferBench

## RCCL-2.13.4 for ROCm 5.4.0
### Changed
- Compatibility with NCCL 2.13.4
- Improvements to RCCL when running with hipGraphs
- RCCL_ENABLE_HIPGRAPH environment variable is no longer necessary to enable hipGraph support
- Minor latency improvements
### Fixed
- Resolved potential memory access error due to asynchronous memset

## RCCL-2.12.10 for ROCm 5.3.0
### Changed
- Improvements to LL128 algorithms
### Added
- Adding initial hipGraph support via opt-in environment variable RCCL_ENABLE_HIPGRAPH
- Integrating with NPKit (https://github.com/microsoft/NPKit) profiling code

## RCCL-2.12.10 for ROCm 5.2.3
### Added
- Compatibility with NCCL 2.12.10
- Packages for test and benchmark executables on all supported OSes using CPack.
- Adding custom signal handler - opt-in with RCCL_ENABLE_SIGNALHANDLER=1
  - Additional details provided if Binary File Descriptor library (BFD) is pre-installed
- Adding support for reusing ports in NET/IB channels
  - Opt-in with NCCL_IB_SOCK_CLIENT_PORT_REUSE=1 and NCCL_IB_SOCK_SERVER_PORT_REUSE=1
  - When "Call to bind failed : Address already in use" error happens in large-scale AlltoAll
    (e.g., >=64 MI200 nodes), users are suggested to opt-in either one or both of the options
    to resolve the massive port usage issue
  - Avoid using NCCL_IB_SOCK_SERVER_PORT_REUSE when NCCL_NCHANNELS_PER_NET_PEER is tuned >1
### Removed
- Removed experimental clique-based kernels

## RCCL-2.11.4 for ROCm 5.2.0
### Changed
- Unit testing framework rework
- Minor bug fixes
### Known issues
- Managed memory is not currently supported for clique-based kernels

## RCCL-2.11.4 for ROCm 5.1.0
### Added
- Compatibility with NCCL 2.11.4
### Known issues
- Managed memory is not currently supported for clique-based kernels

## RCCL-2.10.3 for ROCm 5.0.0
### Added
- Compatibility with NCCL 2.10.3
### Known issues
- Managed memory is not currently supported for clique-based kernels

## RCCL-2.9.9 for ROCm 4.5.0
### Changed
- Packaging split into a runtime package called rccl and a development package called rccl-devel. The development package depends on runtime. The runtime package suggests the development package for all supported OSes except CentOS 7 to aid in the transition. The suggests feature in packaging is introduced as a deprecated feature and will be removed in a future rocm release.
### Added
- Compatibility with NCCL 2.9.9
### Known issues
- Managed memory is not currently supported for clique-based kernels

## [RCCL-2.8.4 for ROCm 4.3.0]
### Added
- Ability to select the number of channels to use for clique-based all reduce (RCCL_CLIQUE_ALLREDUCE_NCHANNELS).  This can be adjusted to tune for performance when computation kernels are being executed in parallel.
### Optimizations
- Additional tuning for clique-based kernel AllReduce performance (still requires opt in with RCCL_ENABLE_CLIQUE=1)
- Modification of default values for number of channels / byte limits for clique-based all reduce based on device architecture
### Changed
- Replaced RCCL_FORCE_ENABLE_CLIQUE to RCCL_CLIQUE_IGNORE_TOPO
- Clique-based kernels can now be enabled on topologies where all active GPUs are XGMI-connected
- Topologies not normally supported by clique-based kernels require RCCL_CLIQUE_IGNORE_TOPO=1
### Fixed
- Install script '-r' flag invoked alone no longer incorrectly deletes any existing builds.
### Known issues
- Managed memory is not currently supported for clique-based kernels

## [RCCL-2.8.4 for ROCm 4.2.0]
### Added
- Compatibility with NCCL 2.8.4

### Optimizations
- Additional tuning for clique-based kernels
- Enabling GPU direct RDMA read from GPU
- Fixing potential memory leak issue when re-creating multiple communicators within same process
- Improved topology detection
### Known issues
- None

## [RCCL-2.7.8 for ROCm 4.1.0]
### Added
- Experimental support for clique-based kernels (opt in with RCCL_ENABLE_CLIQUE=1)
- Clique-based kernels may offer better performance for smaller input sizes
- Clique-based kernels are currently only enabled for AllReduce under a certain byte limit (controlled via RCCL_CLIQUE_ALLREDUCE_BYTE_LIMIT)
### Optimizations
- Performance improvements for Rome-based systems
### Known issues
- Clique-based kernels are currently experimental and have not been fully tested on all topologies.  By default, clique-based kernels are disabled if the detected topology is not supported (override with RCCL_FORCE_ENABLE_CLIQUE)
- Clique-based kernels may hang if there are differences between environment variables set across ranks.
- Clique-based kernels may fail if the input / output device pointers are not the base device pointers returned by hipMalloc.


## [RCCL-2.7.8 for ROCm 3.9.0]
### Added
- Adding support for alltoallv RCCL kernel
### Optimizations
- Modifications to topology based on XGMI links
### Known issues
- None

## [RCCL-2.7.6 for ROCm 3.8.0]
### Added
- Support for static library builds
### Known issues
- None

## [RCCL-2.7.6 for ROCm 3.7.0]
### Added
- Updated to RCCL API version of 2.7.6
- Added gather, scatter and all-to-all collectives

## [RCCL-2.7.0 for ROCm 3.6.0]
### Added
- Updated to RCCL API version of 2.6.4

## [RCCL-2.7.0 for ROCm 3.5.0]
### Added
- Compatibility with NCCL 2.6
- Network interface improvements with API v3
### Optimizations
- Fixing issues and built time improvements for hip-clang
- Network topology detection
- Improved CPU type detection
- Infiniband adaptive routing support
### Changed
- Switched to hip-clang as default compiler
### Deprecated
- Deprecated hcc build