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Fold validateIpcDomainSpansWorld into getIpcDomainNranks

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getIpcDomainNranks now performs the range / world-size / rank checks
itself and throws on violation, so the separate
validateIpcDomainSpansWorld helper is unnecessary. Update the 3 NVLS
callsites (block_pipeline, warp_pipeline, nvls_zero_copy) to call
getIpcDomainNranks directly. The non-NVLS callers also pick up the
strict validation, which is fine because they are only invoked in
single-host or multi-host MNNVL scenarios where worldSize ==
ipcDomainNranks (the NCCL adapter's multi-node path returns nullptr,
falling back to NCCL/RCCL).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Binyang Li
2026-05-06 21:49:48 +00:00
parent 307a471888
commit f0c6ac081f
5 changed files with 8 additions and 22 deletions
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2
src/ext/collectives/allreduce/allreduce_nvls_block_pipeline.cu
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@@ -178,7 +178,7 @@ struct NvlsBlockPipelineAdapter {
void AllreduceNvlsBlockPipeline::initialize(std::shared_ptr<Communicator> comm) {
nSwitchChannels_ = 8;
ipcDomainNranks_ = validateIpcDomainSpansWorld(comm);
ipcDomainNranks_ = getIpcDomainNranks(comm);
// Block-pipeline device-side semaphore indices grow as 6 * ipcDomainNranks (see kernel).
if (6 * ipcDomainNranks_ > NUM_SEMAPHORES) {
throw Error("AllreduceNvlsBlockPipeline: ipcDomainNranks " + std::to_string(ipcDomainNranks_) +

2
src/ext/collectives/allreduce/allreduce_nvls_warp_pipeline.cu
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@@ -142,7 +142,7 @@ struct NvlsWarpPipelineAdapter {
void AllreduceNvlsWarpPipeline::initialize(std::shared_ptr<Communicator> comm) {
nSwitchChannels_ = NUM_NVLS_CONNECTION;
ipcDomainNranks_ = validateIpcDomainSpansWorld(comm);
ipcDomainNranks_ = getIpcDomainNranks(comm);
// The warp-pipeline kernel addresses 2 * nPeers entries per block in `memoryChannels`,
// so per-peer base channel allocation must be at least `2 * nBlocks`. Default
// nBlocks = 4 * ipcDomainNranks (see allreduceKernelFunc), so size accordingly.

2
src/ext/collectives/allreduce/allreduce_nvls_zero_copy.cu
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@@ -105,7 +105,7 @@ void AllreduceNvls::initialize(std::shared_ptr<mscclpp::Communicator> comm) {
MSCCLPP_CUDATHROW(cudaGetDeviceProperties(&deviceProp, device));
computeCapabilityMajor_ = deviceProp.major;
nSwitchChannels_ = 32;
validateIpcDomainSpansWorld(comm);
getIpcDomainNranks(comm);
this->conns_ = setupConnections(comm);
// setup semaphores
std::vector<std::shared_ptr<mscclpp::MemoryDevice2DeviceSemaphore>> memorySemaphores =

9
src/ext/collectives/collective_utils.cc
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@@ -75,14 +75,7 @@ std::vector<std::shared_ptr<mscclpp::MemoryDevice2DeviceSemaphore>> setupMemoryS
int getIpcDomainNranks(std::shared_ptr<mscclpp::Communicator> comm) {
const int envValue = mscclpp::env()->ipcDomainNranks;
if (envValue > 0) {
return envValue;
}
return comm->bootstrap()->getNranksPerNode();
}
int validateIpcDomainSpansWorld(std::shared_ptr<mscclpp::Communicator> comm) {
const int ipcDomainNranks = getIpcDomainNranks(comm);
const int ipcDomainNranks = (envValue > 0) ? envValue : comm->bootstrap()->getNranksPerNode();
const int worldSize = comm->bootstrap()->getNranks();
const int rank = comm->bootstrap()->getRank();
if (ipcDomainNranks < 2 || ipcDomainNranks > MAX_IPC_DOMAIN_NRANKS) {

15
src/ext/collectives/include/collective_utils.hpp
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@@ -51,18 +51,11 @@ std::vector<Connection> setupConnections(std::shared_ptr<Communicator> comm);
std::vector<std::shared_ptr<MemoryDevice2DeviceSemaphore>> setupMemorySemaphores(
std::shared_ptr<Communicator> comm, const std::vector<Connection>& connections, int nChannelsPerConnection);
/// Number of ranks that participate in the same GPU-IPC-reachable peer group (e.g. a single host or
/// a Multi-Node NVLink fabric, or an AMD XGMI domain). Returns the value of `MSCCLPP_IPC_DOMAIN_NRANKS`
/// if set to a positive value; otherwise falls back to `bootstrap->getNranksPerNode()`. This is
/// intentionally independent of `Bootstrap::getNranksPerNode()` so that algorithms can opt in to
/// MNNVL-like behavior without changing the meaning of bootstrap-level APIs.
int getIpcDomainNranks(std::shared_ptr<Communicator> comm);
/// Validates that the IPC domain spans the whole communicator and that the local rank fits within
/// the supported `[2, MAX_IPC_DOMAIN_NRANKS]` range. Used by NVLS allreduce algorithms whose
/// multicast group spans the whole communicator. Returns the validated `ipcDomainNranks`; throws
/// Returns the IPC-reachable peer-group size, validated to span the whole communicator and
/// to be within `[2, MAX_IPC_DOMAIN_NRANKS]`. Reads `MSCCLPP_IPC_DOMAIN_NRANKS` if set to a
/// positive value; otherwise falls back to `bootstrap->getNranksPerNode()`. Throws
/// `Error(InvalidUsage)` on violation.
int validateIpcDomainSpansWorld(std::shared_ptr<Communicator> comm);
int getIpcDomainNranks(std::shared_ptr<Communicator> comm);
std::shared_ptr<DeviceHandle<MemoryChannel>> setupMemoryChannelDeviceHandles(
const std::vector<MemoryChannel>& memoryChannels);