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# Environment variables

The rocBLAS environment variables are collected in the following tables.

Environment variable | Default value | Links | Value
--- | --- | --- | ---

`ROCBLAS_USE_HIPBLASLT`
Provides manual control over which GEMM backend is used.

Unset by default.

Control the GEMM backend

Unset: GEMM backend is automatically selected.
0: Tensile is always used as the GEMM backend.
1: hipBLASLt is preferred as the GEMM backend, but will fallback to Tensile on problems for which hipBLASLt does not provide a solution or when errors are encountered using the hipBLASLt backend.

`ROCBLAS_USE_HIPBLASLT_BATCHED`
Manual control to selectively disable the use of hipBlasLt only for the batched GEMMs. `ROCBLAS_USE_HIPBLASLT=0` disables the `ROCBLAS_USE_HIPBLASLT_BATCHED` variable, because hipBlasLt would not be enabled.

1

Control the GEMM backend

Unset: GEMM batched default backend.
0: Tensile is always used as the GEMM batched backend.
1: hipBLASLt will be used as the GEMM batched backend when applicable, but will fallback to Tensile on problems for which hipBLASLt does not provide a solution or when errors are encountered using the hipBLASLt backend.

`ROCBLAS_DEVICE_MEMORY_SIZE` Sets how much memory to preallocate. | Unset by default. | rocblas_device_memory_size | 0 or unset: Lets rocBLAS manage the device memory. Bigger than 0: Sets the default handle device memory size to the specified size (in bytes).
`ROCBLAS_DEFAULT_ATOMICS_MODE` Sets the default atomics mode during the creation of `rocblas_handle`. | Unset by default. | Atomic operations | 0: Sets the default to `rocblas_atomics_not_allowed` 1: Sets the default to `rocblas_atomics_allowed`
`ROCBLAS_STREAM_ORDER_ALLOC` Allows memory allocation and deallocation to be stream ordered. | 0 | stream order alloc | 0: Disable 1: Enable
`ROCBLAS_BENCH_STREAM_SYNC` Benchmark timing based on `hipStreamSynchronize`, otherwise uses default `hipEvent_t` based timing. | 0 | rocblas-bench timing | 0: Disable 1: Enable

## Logging environment variables

The logging environment variables in rocBLAS are collected in the following table. For information on how to use these variables, see rocBLAS logging.