HcclRecv

Applicability

Product	Supported
Atlas A3 training products / Atlas A3 inference products	√
Atlas A2 training products / Atlas A2 inference products	√
Atlas 200I/500 A2 inference products	☓
Atlas inference products	☓
Atlas training products	√

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

Description

Receives data from the source rank to the specified location on the current rank.

Prototype

      
           HcclResult HcclRecv(void* recvBuf, uint64_t count, HcclDataType dataType, uint32_t srcRank, HcclComm comm, aclrtStream stream)

Parameters

Parameter	Input/Output	Description
recvBuf	Input	Address of the receive buffer.
count	Input	Number of received data records.
dataType	Input	Data type of the data to be received, which is of the HcclDataType type. Atlas A3 training products / Atlas A3 inference products : The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, float64, and bfp16. Atlas A2 training products / Atlas A2 inference products : The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, float64, and bfp16. Atlas training products : The supported data types are int8, uint8, int16, uint16, int32, uint32, int64, uint64, float16, float32, and float64.
srcRank	Input	ID of the source rank in the communicator.
comm	Input	Communicator where the operation is performed.
stream	Input	Stream of the rank.

Returns

HcclResult: HCCL_SUCCESS on success; else, failure.

Constraints

The HcclSend and HcclRecv interfaces are invoked synchronously and must be used in pairs. That is, after a process calls the HcclSend interface, the process can call the next interface only after the corresponding HcclRecv interface receives data, as shown in the following figure.

Example

      
       
         
         
           void *sendBuf = nullptr;
void *recvBuf = nullptr;
uint64_t count = 8;
size_t mallocSize = count * sizeof(float);

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

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

// Perform the Send/Recv operation. Devices 0, 2, 4, and 6 send data, and devices 1, 3, 5, and 7 receive data.
// The HcclSend and HcclRecv APIs are called synchronously and must be used in pairs.
if (deviceId % 2 == 0) {
    // Allocate the device memory for storing the input data.
    aclrtMalloc(&sendBuf, mallocSize, ACL_MEM_MALLOC_HUGE_ONLY);
    // Initialize the input data.
    aclrtMemcpy(sendBuf, mallocSize, hostBuf, mallocSize, ACL_MEMCPY_HOST_TO_DEVICE);
    // Perform the Send operation.
    HcclSend(sendBuf, count, HCCL_DATA_TYPE_FP32, deviceId + 1, hcclComm, stream);
} else {
    // Allocate the device memory for receiving data.
    aclrtMalloc(&recvBuf, mallocSize, ACL_MEM_MALLOC_HUGE_ONLY);
    // Perform the Recv operation.
    HcclRecv(recvBuf, count, HCCL_DATA_TYPE_FP32, deviceId - 1, 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: Point-to-Point Communication