aclrtMallocHost

Applicability

Description

Allocates the host memory (lock page memory). The system ensures that the start address of the memory is 64-byte aligned.

For the Ascend RC form, the host and device are integrated. Therefore, allocating the host memory is equivalent to allocating the device memory. In addition, memory is allocated based on normal pages. If the start address needs to be 64-byte aligned, you need to handle the alignment problem by yourself.

Prototype

aclError aclrtMallocHost(void **hostPtr, size_t size)

Parameters

Returns

0 on success; else, failure. For details, see aclError.

Restrictions

• The memory allocated by this API is not initialized. Before using the memory, call aclrtMemset to initialize it and clear its random numbers.
• This API does not perform implicit device synchronization or stream synchronization. The memory allocation result, either success or failure, is returned immediately.
• Memory allocated by the aclrtMallocHost call needs to be freed by the aclrtFreeHost call.
• If aclrtMallocHost is called to allocate too much lock page memory, the physical memory used by the operating system for paging decreases, and the overall system performance deteriorates.
• Performance deterioration will be caused by too frequent calls to aclrtMallocHost and aclrtFreeHost. You are advised to allocate or manage memory in advance to avoid unnecessary memory allocation and deallocation.
• For the Ascend RC form and Open Ctrl CPU form, if you use this API to allocate a large memory block and divide and manage the memory, each memory segment must meet the requirements listed below. len indicates the size of a memory segment. ALIGN_UP[len,k] indicates rounding up to a multiple of k bytes as in this formula: ((len – 1)/k + 1) x k.
  • The memory size is rounded up to the nearest multiple of 32 plus 32 bytes (m = ALIGN_UP[len,32] + 32 bytes).
  • The memory start address must be 64-byte aligned (ALIGN_UP[m,64]).

See Also

For the API call example, see Data Transfer.