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[UR][CUDA] Fix device to device copies in... #21277

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[UR][CUDA] Fix device to device copies in... #21277

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39 changes: 35 additions & 4 deletions unified-runtime/source/adapters/cuda/usm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -574,10 +574,41 @@ urUSMPoolTrimToExp(ur_context_handle_t hContext, ur_device_handle_t hDevice,
return UR_RESULT_SUCCESS;
}

UR_APIEXPORT ur_result_t UR_APICALL urUSMContextMemcpyExp(ur_context_handle_t,
void *pDst,
const void *pSrc,
size_t Size) {
UR_APIEXPORT ur_result_t UR_APICALL urUSMContextMemcpyExp(
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@pbalcer pbalcer Feb 16, 2026

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This is not a performance-critical function. Can we just always synchronize at the end? Would make the code simpler.

ur_context_handle_t hContext, void *pDst, const void *pSrc, size_t Size) {

CUmemorytype memTypeDst;
UR_CHECK_ERROR(cuPointerGetAttribute(
&memTypeDst, CU_POINTER_ATTRIBUTE_MEMORY_TYPE, (CUdeviceptr)pDst));

CUmemorytype memTypeSrc;
UR_CHECK_ERROR(cuPointerGetAttribute(
&memTypeSrc, CU_POINTER_ATTRIBUTE_MEMORY_TYPE, (CUdeviceptr)pSrc));

if (memTypeDst != CU_MEMORYTYPE_DEVICE ||
memTypeSrc != CU_MEMORYTYPE_DEVICE) {
UR_CHECK_ERROR(cuMemcpy((CUdeviceptr)pDst, (CUdeviceptr)pSrc, Size));
return UR_RESULT_SUCCESS;
}

// For device to device copy, we need to synchronize the host with the memcpy
// operation to ensure the copy is completed.
// For details, see:
// https://docs.nvidia.com/cuda/cuda-driver-api/api-sync-behavior.html.
unsigned int devIdx = 0;
UR_CHECK_ERROR(cuPointerGetAttribute(
&devIdx, CU_POINTER_ATTRIBUTE_DEVICE_ORDINAL, (CUdeviceptr)pDst));
if (devIdx >= hContext->getDevices().size()) {
return UR_RESULT_ERROR_INVALID_CONTEXT;
}

// Device ordinal obtained using cuPointerGetAttribute corresponds to the
// device index in the context's device list.
ur_device_handle_t owningDev = hContext->getDevices()[devIdx];

ScopedContext Active(owningDev);
UR_CHECK_ERROR(cuMemcpy((CUdeviceptr)pDst, (CUdeviceptr)pSrc, Size));
UR_CHECK_ERROR(cuCtxSynchronize());

return UR_RESULT_SUCCESS;
}
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