Device Memory Allocation in rocBLAS#

The following computational functions use temporary device memory.


Use of temporary device memory

L1 reduction functions

  • rocblas_Xasum

  • rocblas_Xasum_batched

  • rocblas_Xasum_strided_batched

  • rocblas_Xdot

  • rocblas_Xdot_batched

  • rocblas_Xdot_strided_batched

  • rocblas_Xmax

  • rocblas_Xmax_batched

  • rocblas_Xmax_strided_batched

  • rocblas_Xmin

  • rocblas_Xmin_batched

  • rocblas_Xmin_strided_batched

  • rocblas_Xnrm2

  • rocblas_Xnrm2_batched

  • rocblas_Xnrm2_strided_batched

  • rocblas_dot_ex

  • rocblas_dot_batched_ex

  • rocblas_dot_strided_batched_ex

  • rocblas_nrm2_ex

  • rocblas_nrm2_batched_ex

  • rocblas_nrm2_strided_batched_ex

Reduction array

L2 functions

  • rocblas_Xgemv (optional)

  • rocblas_Xgemv_batched

  • rocblas_Xgemv_strided_batched

  • rocblas_Xtbmv

  • rocblas_Xtbmv_batched

  • rocblas_Xtbmv_strided_batched

  • rocblas_Xtpmv

  • rocblas_Xtpmv_batched

  • rocblas_Xtpmv_strided_batched

  • rocblas_Xtrmv

  • rocblas_Xtrmv_batched

  • rocblas_Xtrmv_strided_batched

  • rocblas_Xtrsv

  • rocblas_Xtrsv_batched

  • rocblas_Xtrsv_strided_batched

  • rocblas_Xhemv

  • rocblas_Xhemv_batched

  • rocblas_Xhemv_strided_batched

  • rocblas_Xsymv

  • rocblas_Xsymv_batched

  • rocblas_Xsymv_strided_batched

  • rocblas_Xtrsv_ex

  • rocblas_Xtrsv_batched_ex

  • rocblas_Xtrsv_strided_batched_ex

Result array before overwriting input

Column reductions of skinny transposed matrices applicable for gemv functions

L3 gemm based functions

  • rocblas_Xtrsm

  • rocblas_Xtrsm_batched

  • rocblas_Xtrsm_strided_batched

  • rocblas_Xsymm

  • rocblas_Xsymm_batched

  • rocblas_Xsymm_strided_batched

  • rocblas_Xsyrk

  • rocblas_Xsyrk_batched

  • rocblas_Xsyrk_strided_batched

  • rocblas_Xsyr2k

  • rocblas_Xsyr2k_batched

  • rocblas_Xsyr2k_strided_batched

  • rocblas_Xsyrkx

  • rocblas_Xsyrkx_batched

  • rocblas_Xsyrkx_strided_batched

  • rocblas_Xtrmm

  • rocblas_Xtrmm_batched

  • rocblas_Xtrmm_strided_batched

  • rocblas_Xhemm

  • rocblas_Xhemm_batched

  • rocblas_Xhemm_strided_batched

  • rocblas_Xherk

  • rocblas_Xherk_batched

  • rocblas_Xherk_strided_batched

  • rocblas_Xher2k

  • rocblas_Xher2k_batched

  • rocblas_Xher2k_strided_batched

  • rocblas_Xherkx

  • rocblas_Xherkx_batched

  • rocblas_Xherkx_strided_batched

  • rocblas_Xgemm

  • rocblas_Xgemm_batched

  • rocblas_Xgemm_strided_batched

  • rocblas_gemm_ex

  • rocblas_gemm_ex_batched

  • rocblas_gemm_ex_strided_batched

  • rocblas_Xtrtri

  • rocblas_Xtrtri_batched

  • rocblas_Xtrtri_strided_batched

Block of matrix


  • rocblas_set_vector

  • rocblas_get_vector

  • rocblas_set_matrix

  • rocblas_get_matrix

Buffer to compress noncontiguous arrays

For temporary device memory, rocBLAS uses a per-handle memory allocation with out-of-band management. The temporary device memory is stored in the handle. This allows for recycling temporary device memory across multiple computational kernels that use the same handle. Each handle has a single stream, and kernels execute in order in the stream, with each kernel completing before the next kernel in the stream starts. There are 4 schemes for temporary device memory:

  1. rocBLAS_managed: This is the default scheme. If there is not enough memory in the handle, computational functions allocate the memory they require. Note that any memory allocated persists in the handle, so it is available for later computational functions that use the handle.

  2. user_managed, preallocate: An environment variable is set before the rocBLAS handle is created, and thereafter there are no more allocations or deallocations.

  3. user_managed, manual: The user calls helper functions to get or set memory size throughout the program, thereby controlling when allocation and deallocation occur.

  4. user_owned: The user allocates workspace and calls a helper function to allow rocBLAS to access the workspace.

The default scheme has the disadvantage that allocation is synchronizing, so if there is not enough memory in the handle, a synchronizing deallocation and allocation occur.

Environment Variable for Preallocating#

The environment variable ROCBLAS_DEVICE_MEMORY_SIZE is used to set how much memory to preallocate:

  • If > 0, sets the default handle device memory size to the specified size (in bytes)

  • If == 0 or unset, lets rocBLAS manage device memory, using a default size (like 32MB), and expanding it when necessary

Functions for Manually Setting Memory Size#

  • rocblas_set_device_memory_size

  • rocblas_get_device_memory_size

  • rocblas_is_user_managing_device_memory

Function for Setting User Owned Workspace#

  • rocblas_set_workspace

Functions for Finding How Much Memory Is Required#

  • rocblas_start_device_memory_size_query

  • rocblas_stop_device_memory_size_query

  • rocblas_is_managing_device_memory

See the API section for information on the above functions.

rocBLAS Function Return Values for Insufficient Device Memory#

If the user preallocates or manually allocates, then that size is used as the limit, and no resizing or synchronizing ever occurs. The following two function return values indicate insufficient memory:

  • rocblas_status == rocblas_status_memory_error : indicates there is not sufficient device memory for a rocBLAS function

  • rocblas_status == rocblas_status_perf_degraded : indicates that a slower algorithm was used because of insufficient device memory for the optimal algorithm

Stream-Ordered Memory Allocation#

Stream-ordered device memory allocation is added to rocBLAS. Asynchronous allocators ( hipMallocAsync() and hipFreeAsync() ) are used to allow allocation and free to be stream order.

This is a non-default beta option enabled by setting the environment variable ROCBLAS_STREAM_ORDER_ALLOC.

A user may check if the device supports stream-order allocation by calling hipDeviceGetAttribute() with device attribute hipDeviceAttributeMemoryPoolsSupported.

Environment Variable to Enable Stream-Ordered Memory Allocation#

On supported platforms, environment variable ROCBLAS_STREAM_ORDER_ALLOC is used to enable stream-ordered memory allocation.

  • if > 0, sets the allocation to be stream-ordered, uses hipMallocAsync/hipFreeAsync to manage device memory.

  • if == 0 or unset, uses hipMalloc/hipFree to manage device memory.

Supports Switching Streams Without Any Synchronization#

Stream-order memory allocation allows switching of streams without the need to call hipStreamSynchronize().