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Fixes and improvements to NCCL user buffer registration feature. #122

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Merged
romerojosh merged 4 commits into from
Apr 30, 2026
Merged

Fixes and improvements to NCCL user buffer registration feature. #122

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81c87e7
Fix NCCL user buffer registration implementation.
romerojosh Apr 29, 2026
536d4e3
Deregister buffers based on presence in ubr_handle map.
romerojosh Apr 30, 2026
c3c55bb
More robust handling of NCCL registration failures in cudecompMalloc.
romerojosh Apr 30, 2026
0f3ca65
Improve communicator lifetime handling for NCCL buffer deregistation.
romerojosh Apr 30, 2026
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2 changes: 1 addition & 1 deletion include/internal/common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ struct cudecompHandle {
cudecomp::ncclComm nccl_comm; // NCCL communicator (global)
cudecomp::ncclComm nccl_local_comm; // NCCL communicator (intra-node, or intra-clique on MNNVL systems)
bool nccl_enable_ubr = false; // Flag to control NCCL user buffer registration usage
std::unordered_map<void*, std::vector<std::pair<ncclComm_t, void*>>>
std::unordered_map<void*, std::vector<std::pair<cudecomp::ncclComm, void*>>>
nccl_ubr_handles; // map of allocated buffer address to NCCL registration handle(s)

std::vector<cudaStream_t> streams; // internal streams for concurrent scheduling
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45 changes: 29 additions & 16 deletions src/cudecomp.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -579,6 +579,15 @@ cudecompResult_t cudecompFinalize(cudecompHandle_t handle) {
try {
checkHandle(handle);

#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 19, 0)
for (auto& entry : handle->nccl_ubr_handles) {
for (const auto& ubr_handle : entry.second) {
CHECK_NCCL(ncclCommDeregister(*ubr_handle.first, ubr_handle.second));
}
}
handle->nccl_ubr_handles.clear();
#endif

handle->nccl_comm.reset();
handle->nccl_local_comm.reset();

Expand Down Expand Up @@ -1195,6 +1204,8 @@ cudecompResult_t cudecompMalloc(cudecompHandle_t handle, cudecompGridDesc_t grid
try {
checkHandle(handle);
checkGridDesc(grid_desc);
if (!buffer) { THROW_INVALID_USAGE("buffer argument cannot be null"); }
if (buffer_size_bytes == 0) { THROW_INVALID_USAGE("buffer size cannot be zero"); }

if (transposeBackendRequiresNvshmem(grid_desc->config.transpose_comm_backend) ||
haloBackendRequiresNvshmem(grid_desc->config.halo_comm_backend)) {
Expand Down Expand Up @@ -1266,14 +1277,20 @@ cudecompResult_t cudecompMalloc(cudecompHandle_t handle, cudecompGridDesc_t grid
haloBackendRequiresNccl(grid_desc->config.halo_comm_backend)) {

if (handle->nccl_enable_ubr) {
void* nccl_ubr_handle;
if (grid_desc->nccl_comm) {
CHECK_NCCL(ncclCommRegister(*grid_desc->nccl_comm, buffer, buffer_size_bytes, &nccl_ubr_handle));
handle->nccl_ubr_handles[*buffer].push_back(std::make_pair(*grid_desc->nccl_comm, nccl_ubr_handle));
}
if (grid_desc->nccl_local_comm) {
CHECK_NCCL(ncclCommRegister(*grid_desc->nccl_local_comm, buffer, buffer_size_bytes, &nccl_ubr_handle));
handle->nccl_ubr_handles[*buffer].push_back(std::make_pair(*grid_desc->nccl_local_comm, nccl_ubr_handle));
try {
void* nccl_ubr_handle;
if (grid_desc->nccl_comm) {
CHECK_NCCL(ncclCommRegister(*grid_desc->nccl_comm, *buffer, buffer_size_bytes, &nccl_ubr_handle));
handle->nccl_ubr_handles[*buffer].push_back(std::make_pair(grid_desc->nccl_comm, nccl_ubr_handle));
}
if (grid_desc->nccl_local_comm) {
CHECK_NCCL(ncclCommRegister(*grid_desc->nccl_local_comm, *buffer, buffer_size_bytes, &nccl_ubr_handle));
handle->nccl_ubr_handles[*buffer].push_back(std::make_pair(grid_desc->nccl_local_comm, nccl_ubr_handle));
}
} catch (...) {
cudecompFree(handle, grid_desc, *buffer);
*buffer = nullptr;
throw;
}
}
}
Expand All @@ -1294,15 +1311,11 @@ cudecompResult_t cudecompFree(cudecompHandle_t handle, cudecompGridDesc_t grid_d
checkGridDesc(grid_desc);

#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 19, 0)
if (transposeBackendRequiresNccl(grid_desc->config.transpose_comm_backend) ||
haloBackendRequiresNccl(grid_desc->config.halo_comm_backend)) {

if (handle->nccl_ubr_handles.count(buffer) != 0) {
for (const auto& entry : handle->nccl_ubr_handles[buffer]) {
CHECK_NCCL(ncclCommDeregister(entry.first, entry.second));
}
handle->nccl_ubr_handles.erase(buffer);
if (handle->nccl_ubr_handles.count(buffer) != 0) {
for (const auto& entry : handle->nccl_ubr_handles[buffer]) {
CHECK_NCCL(ncclCommDeregister(*entry.first, entry.second));
}
handle->nccl_ubr_handles.erase(buffer);
}
#endif

Expand Down
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