6.32. Peer Context Memory Access

This section describes the direct peer context memory access functions of the low-level CUDA driver application programming interface.

Functions

CUresult cuCtxDisablePeerAccess(CUcontext peerContext): Disables direct access to memory allocations in a peer context and unregisters any registered allocations.
CUresult cuCtxEnablePeerAccess(CUcontext peerContext, unsigned int Flags): Enables direct access to memory allocations in a peer context.
CUresult cuDeviceCanAccessPeer(int *canAccessPeer, CUdevice dev, CUdevice peerDev): Queries if a device may directly access a peer device's memory.
CUresult cuDeviceGetP2PAtomicCapabilities(unsigned int *capabilities, const CUatomicOperation *operations, unsigned int count, CUdevice srcDevice, CUdevice dstDevice): Queries details about atomic operations supported between two devices.
CUresult cuDeviceGetP2PAttribute(int *value, CUdevice_P2PAttribute attrib, CUdevice srcDevice, CUdevice dstDevice): Queries attributes of the link between two devices.

6.32.1. Functions

CUresult cuCtxDisablePeerAccess(CUcontext peerContext)

Disables direct access to memory allocations in a peer context and unregisters any registered allocations.

Returns CUDA_ERROR_PEER_ACCESS_NOT_ENABLED if direct peer access has not yet been enabled from peerContext to the current context.

Returns CUDA_ERROR_INVALID_CONTEXT if there is no current context, or if peerContext is not a valid context.

See also

cuDeviceCanAccessPeer, cuCtxEnablePeerAccess, ::cudaDeviceDisablePeerAccess

Note

Note that this function may also return error codes from previous, asynchronous launches.

Parameters: peerContext – - Peer context to disable direct access to
Returns: CUDA_SUCCESS, CUDA_ERROR_DEINITIALIZED, CUDA_ERROR_NOT_INITIALIZED, CUDA_ERROR_PEER_ACCESS_NOT_ENABLED, CUDA_ERROR_INVALID_CONTEXT,

CUresult cuCtxEnablePeerAccess(CUcontext peerContext, unsigned int Flags)

Enables direct access to memory allocations in a peer context.

If both the current context and peerContext are on devices which support unified addressing (as may be queried using CU_DEVICE_ATTRIBUTE_UNIFIED_ADDRESSING) and same major compute capability, then on success all allocations from peerContext will immediately be accessible by the current context. See Unified Addressing for additional details.

Note that access granted by this call is unidirectional and that in order to access memory from the current context in peerContext, a separate symmetric call to cuCtxEnablePeerAccess() is required.

Note that there are both device-wide and system-wide limitations per system configuration, as noted in the CUDA Programming Guide under the section “Peer-to-Peer Memory Access”.

Returns CUDA_ERROR_PEER_ACCESS_UNSUPPORTED if cuDeviceCanAccessPeer() indicates that the CUdevice of the current context cannot directly access memory from the CUdevice of peerContext.

Returns CUDA_ERROR_PEER_ACCESS_ALREADY_ENABLED if direct access of peerContext from the current context has already been enabled.

Returns CUDA_ERROR_TOO_MANY_PEERS if direct peer access is not possible because hardware resources required for peer access have been exhausted.

Returns CUDA_ERROR_INVALID_CONTEXT if there is no current context, peerContext is not a valid context, or if the current context is peerContext.

Returns CUDA_ERROR_INVALID_VALUE if Flags is not 0.

See also

cuDeviceCanAccessPeer, cuCtxDisablePeerAccess, ::cudaDeviceEnablePeerAccess

Note

Note that this function may also return error codes from previous, asynchronous launches.

Parameters

peerContext – - Peer context to enable direct access to from the current context
Flags – - Reserved for future use and must be set to 0

Returns

CUDA_SUCCESS, CUDA_ERROR_DEINITIALIZED, CUDA_ERROR_NOT_INITIALIZED, CUDA_ERROR_PEER_ACCESS_ALREADY_ENABLED, CUDA_ERROR_TOO_MANY_PEERS, CUDA_ERROR_INVALID_CONTEXT, CUDA_ERROR_PEER_ACCESS_UNSUPPORTED, CUDA_ERROR_INVALID_VALUE

CUresult cuDeviceCanAccessPeer(int *canAccessPeer, CUdevice dev, CUdevice peerDev)

Queries if a device may directly access a peer device’s memory.

Returns in *canAccessPeer a value of 1 if contexts on dev are capable of directly accessing memory from contexts on peerDev and 0 otherwise. If direct access of peerDev from dev is possible, then access may be enabled on two specific contexts by calling cuCtxEnablePeerAccess().

See also

cuCtxEnablePeerAccess, cuCtxDisablePeerAccess, ::cudaDeviceCanAccessPeer

Note

Note that this function may also return error codes from previous, asynchronous launches.

Parameters

canAccessPeer – - Returned access capability
dev – - Device from which allocations on peerDev are to be directly accessed.
peerDev – - Device on which the allocations to be directly accessed by dev reside.

Returns

CUDA_SUCCESS, CUDA_ERROR_DEINITIALIZED, CUDA_ERROR_NOT_INITIALIZED, CUDA_ERROR_INVALID_DEVICE

CUresult cuDeviceGetP2PAtomicCapabilities(unsigned int *capabilities, const CUatomicOperation *operations, unsigned int count, CUdevice srcDevice, CUdevice dstDevice)

Queries details about atomic operations supported between two devices.

Returns in *capabilities the details about requested atomic *operations over the the link between srcDevice and dstDevice. The allocated size of *operations and *capabilities must be count.

For each CUatomicOperation in *operations, the corresponding result in *capabilities will be a bitmask indicating which of CUatomicOperationCapability the link supports natively.

Returns CUDA_ERROR_INVALID_DEVICE if srcDevice or dstDevice are not valid or if they represent the same device.

Returns CUDA_ERROR_INVALID_VALUE if *capabilities or *operations is NULL, if count is 0, or if any of *operations is not valid.

See also

cuDeviceGetP2PAttribute, ::cudaDeviceGetP2PAttribute, ::cudaDeviceGetP2PAtomicCapabilities

Note

Note that this function may also return error codes from previous, asynchronous launches.

Parameters

capabilities – - Returned capability details of each requested operation
operations – - Requested operations
count – - Count of requested operations and size of capabilities
srcDevice – - The source device of the target link
dstDevice – - The destination device of the target link

Returns

CUDA_SUCCESS, CUDA_ERROR_INVALID_DEVICE, CUDA_ERROR_INVALID_VALUE

CUresult cuDeviceGetP2PAttribute(int *value, CUdevice_P2PAttribute attrib, CUdevice srcDevice, CUdevice dstDevice)

Queries attributes of the link between two devices.

Returns in *value the value of the requested attribute attrib of the link between srcDevice and dstDevice. The supported attributes are:

CU_DEVICE_P2P_ATTRIBUTE_PERFORMANCE_RANK: A relative value indicating the performance of the link between two devices.
CU_DEVICE_P2P_ATTRIBUTE_ACCESS_SUPPORTED P2P: 1 if P2P Access is enable.
CU_DEVICE_P2P_ATTRIBUTE_NATIVE_ATOMIC_SUPPORTED: 1 if all CUDA-valid atomic operations over the link are supported.
CU_DEVICE_P2P_ATTRIBUTE_CUDA_ARRAY_ACCESS_SUPPORTED: 1 if cudaArray can be accessed over the link.
CU_DEVICE_P2P_ATTRIBUTE_ONLY_PARTIAL_NATIVE_ATOMIC_SUPPORTED: 1 if some CUDA-valid atomic operations over the link are supported. Information about specific operations can be retrieved with cuDeviceGetP2PAtomicCapabilities.

Returns CUDA_ERROR_INVALID_DEVICE if srcDevice or dstDevice are not valid or if they represent the same device.

Returns CUDA_ERROR_INVALID_VALUE if attrib is not valid or if value is a null pointer.

Note

Note that this function may also return error codes from previous, asynchronous launches.

Parameters

value – - Returned value of the requested attribute
attrib – - The requested attribute of the link between srcDevice and dstDevice.
srcDevice – - The source device of the target link.
dstDevice – - The destination device of the target link.

Returns

CUDA_SUCCESS, CUDA_ERROR_DEINITIALIZED, CUDA_ERROR_NOT_INITIALIZED, CUDA_ERROR_INVALID_DEVICE, CUDA_ERROR_INVALID_VALUE