HcclBroadcast

Applicability

Product	Supported
Atlas 350 Accelerator Card	√
Atlas A3 training product/Atlas A3 inference product	√
Atlas A2 training product/Atlas A2 inference product	√
Atlas 200I/500 A2 inference product	☓
Atlas inference product	☓
Atlas training product	√

For Atlas A2 training product/Atlas A2 inference product, only the Atlas 800T A2 training server, Atlas 900 A2 PoD cluster basic unit, and Atlas 200T A2 Box16 heterogeneous subrack are supported.

Function

Broadcasts the data of the root rank in the communicator to other ranks.

Prototype

HcclResult HcclBroadcast(void *buf, uint64_t count, HcclDataType dataType, uint32_t root, HcclComm comm, aclrtStream stream)

Parameters

Parameter	Input/Output	Description
buf	Input/Output	Data buffer, used as a send buffer for root ranks, while a receive buffer for non-root ranks.
count	Input	Number of data records to perform Broadcast operation. For example, if only one int32 data record is involved, then count=1.
dataType	Input	Data type of the Broadcast operation, which is of the HcclDataType type. Atlas 350 Accelerator Card: The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float8-e5m2, float8-e4m3, float8-e8m0, hifloat8, float16, float32, float64, and bfp16. Atlas A3 training product/Atlas A3 inference product: The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, float64, and bfp16. Atlas A2 training product/Atlas A2 inference product: The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, float64, and bfp16. Atlas training product: The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, and float64.
root	Input	ID of the root rank.
comm	Input	Communicator where the operation is performed.
stream	Input	Stream of the rank.

Returns

HcclResult: HCCL_SUCCESS on success, or else failure.

Constraints

The ranks must have the same count, dataType, and root.
There can be only one root rank globally.

Call Example

// Allocate device memory for collective communication.
void *buf = nullptr;    // Data buffer, used as a send buffer for root ranks, while a receive buffer for non-root ranks.
uint64_t count = 8;     // Number of data elements involved in the broadcast operation.
size_t mallocSize = count * sizeof(float);
aclrtMalloc(&buf, mallocSize, ACL_MEM_MALLOC_HUGE_ONLY);

// Construct the input data on the root rank.
if (deviceId == rootRank) {    
    aclrtMemcpy(buf, mallocSize, hostBuf, mallocSize, ACL_MEMCPY_HOST_TO_DEVICE);
}

// Initialize the communicator.
uint32_t rankSize = 8;
HcclComm hcclComm;
HcclCommInitRootInfo(rankSize, &rootInfo, deviceId, &hcclComm);

// Create a task flow.
aclrtStream stream;
aclrtCreateStream(&stream);

// Perform the broadcast operation to broadcast the data of the root rank in the communicator to other ranks.
HcclBroadcast(buf, count, HCCL_DATA_TYPE_FP32, rootRank, hcclComm, stream);
// Wait until the collective communication task in the task flow is complete.
aclrtSynchronizeStream(stream);

// Free resources.
aclrtFree(sendBuf);          // Free the device memory.
aclrtFree(recvBuf);          // Free the device memory.
aclrtDestroyStream(stream);  // Destroy the task flow.
HcclCommDestroy(hcclComm);   // Destroy the communicator.

Parent topic: Collective Communication