6.30. Peer Device Memory Access

This section describes the peer device memory access functions of the CUDA runtime application programming interface.

Functions

__host__ cudaError_t cudaDeviceCanAccessPeer(int *canAccessPeer, int device, int peerDevice)

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

__host__ cudaError_t cudaDeviceDisablePeerAccess(int peerDevice)

Disables direct access to memory allocations on a peer device.

__host__ cudaError_t cudaDeviceEnablePeerAccess(int peerDevice, unsigned int flags)

Enables direct access to memory allocations on a peer device.

6.30.1. Functions

__host__ cudaError_t cudaDeviceCanAccessPeer(int *canAccessPeer, int device, int peerDevice)

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

Returns in *canAccessPeer a value of 1 if device device is capable of directly accessing memory from peerDevice and 0 otherwise. If direct access of peerDevice from device is possible, then access may be enabled by calling cudaDeviceEnablePeerAccess().

See also

cudaDeviceEnablePeerAccess, cudaDeviceDisablePeerAccess, ::cuDeviceCanAccessPeer

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Parameters

• canAccessPeer – - Returned access capability

• device – - Device from which allocations on peerDevice are to be directly accessed.

• peerDevice – - Device on which the allocations to be directly accessed by device reside.

Returns

cudaSuccess, cudaErrorInvalidDevice

__host__ cudaError_t cudaDeviceDisablePeerAccess(int peerDevice)

Disables direct access to memory allocations on a peer device.

Returns cudaErrorPeerAccessNotEnabled if direct access to memory on peerDevice has not yet been enabled from the current device.

See also

cudaDeviceCanAccessPeer, cudaDeviceEnablePeerAccess, ::cuCtxDisablePeerAccess

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Parameters

peerDevice – - Peer device to disable direct access to

Returns

cudaSuccess, cudaErrorPeerAccessNotEnabled, cudaErrorInvalidDevice

__host__ cudaError_t cudaDeviceEnablePeerAccess(int peerDevice, unsigned int flags)

Enables direct access to memory allocations on a peer device.

On success, all allocations from peerDevice will immediately be accessible by the current device. They will remain accessible until access is explicitly disabled using cudaDeviceDisablePeerAccess() or either device is reset using cudaDeviceReset().

Note that access granted by this call is unidirectional and that in order to access memory on the current device from peerDevice, a separate symmetric call to cudaDeviceEnablePeerAccess() 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 cudaErrorInvalidDevice if cudaDeviceCanAccessPeer() indicates that the current device cannot directly access memory from peerDevice.

Returns cudaErrorPeerAccessAlreadyEnabled if direct access of peerDevice from the current device has already been enabled.

Returns cudaErrorInvalidValue if flags is not 0.

See also

cudaDeviceCanAccessPeer, cudaDeviceDisablePeerAccess, ::cuCtxEnablePeerAccess

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Parameters

• peerDevice – - Peer device to enable direct access to from the current device

• flags – - Reserved for future use and must be set to 0

Returns

cudaSuccess, cudaErrorInvalidDevice, cudaErrorPeerAccessAlreadyEnabled, cudaErrorInvalidValue