Functions
cudaError_t
cudaPointerGetAttributes
(struct
cudaPointerAttributes
*attributes, const void
*ptr)
Returns
attributes
about
a
specified
pointer.
Detailed
Description
\brief unified addressing functions of the CUDA runtime API (cuda_runtime_api.h)
This section describes the unified addressing functions of the CUDA runtime application
programming interface.
Overview
CUDA devices can share a unified address space with the host. For these devices there is
no distinction between a device pointer and a host pointer -- the same pointer value may
be used to access memory from the host program and from a kernel running on the device
(with exceptions enumerated below).
Supported
Platforms
Whether or not a device supports unified addressing may be queried by calling
cudaGetDeviceProperties() with the device property cudaDeviceProp::unifiedAddressing.
Unified addressing is automatically enabled in 64-bit processes .
Unified addressing is not yet supported on Windows Vista or Windows 7 for devices that do
not use the TCC driver model.
Looking
Up
Information
from
Pointer
Values
It is possible to look up information about the memory which backs a pointer value. For
instance, one may want to know if a pointer points to host or device memory. As another
example, in the case of device memory, one may want to know on which CUDA device the
memory resides. These properties may be queried using the function
cudaPointerGetAttributes()
Since pointers are unique, it is not necessary to specify information about the pointers
specified to cudaMemcpy() and other copy functions. The copy direction cudaMemcpyDefault
may be used to specify that the CUDA runtime should infer the location of the pointer from
its value.
Automatic
Mapping
of
Host
Allocated
Host
Memory
All host memory allocated through all devices using cudaMallocHost() and cudaHostAlloc()
is always directly accessible from all devices that support unified addressing. This is
the case regardless of whether or not the flags cudaHostAllocPortable and
cudaHostAllocMapped are specified.
The pointer value through which allocated host memory may be accessed in kernels on all
devices that support unified addressing is the same as the pointer value through which
that memory is accessed on the host. It is not necessary to call
cudaHostGetDevicePointer() to get the device pointer for these allocations.
Note that this is not the case for memory allocated using the flag
cudaHostAllocWriteCombined, as discussed below.
Direct
Access
of
Peer
Memory
Upon enabling direct access from a device that supports unified addressing to another peer
device that supports unified addressing using cudaDeviceEnablePeerAccess() all memory
allocated in the peer device using cudaMalloc() and cudaMallocPitch() will immediately be
accessible by the current device. The device pointer value through which any peer's memory
may be accessed in the current device is the same pointer value through which that memory
may be accessed from the peer device.
Exceptions,
Disjoint
Addressing
Not all memory may be accessed on devices through the same pointer value through which
they are accessed on the host. These exceptions are host memory registered using
cudaHostRegister() and host memory allocated using the flag cudaHostAllocWriteCombined.
For these exceptions, there exists a distinct host and device address for the memory. The
device address is guaranteed to not overlap any valid host pointer range and is guaranteed
to have the same value across all devices that support unified addressing.
This device address may be queried using cudaHostGetDevicePointer() when a device using
unified addressing is current. Either the host or the unified device pointer value may be
used to refer to this memory in cudaMemcpy() and similar functions using the
cudaMemcpyDefault memory direction.
Function
Documentation
cudaError_t cudaPointerGetAttributes (struct cudaPointerAttributes * attributes, const void *
Returns in *attributes the attributes of the pointer ptr. If pointer was not allocated in,
mapped by or registered with context supporting unified addressing cudaErrorInvalidValue
is returned.
The cudaPointerAttributes structure is defined as:
struct cudaPointerAttributes {
enum cudaMemoryType memoryType;
int device;
void *devicePointer;
void *hostPointer;
int isManaged;
In this structure, the individual fields mean
• memoryType identifies the physical location of the memory associated with pointer ptr.
It can be cudaMemoryTypeHost for host memory or cudaMemoryTypeDevice for device memory.
• device is the device against which ptr was allocated. If ptr has memory type
cudaMemoryTypeDevice then this identifies the device on which the memory referred to by
ptr physically resides. If ptr has memory type cudaMemoryTypeHost then this identifies
the device which was current when the allocation was made (and if that device is
deinitialized then this allocation will vanish with that device's state).
• devicePointer is the device pointer alias through which the memory referred to by ptr
may be accessed on the current device. If the memory referred to by ptr cannot be
accessed directly by the current device then this is NULL.
• hostPointer is the host pointer alias through which the memory referred to by ptr may be
accessed on the host. If the memory referred to by ptr cannot be accessed directly by
the host then this is NULL.
• isManaged indicates if the pointer ptr points to managed memory or not.
Parameters:
attributes - Attributes for the specified pointer
ptr - Pointer to get attributes for
Returns:
cudaSuccess, cudaErrorInvalidDevice, cudaErrorInvalidValue
See also:
cudaGetDeviceCount, cudaGetDevice, cudaSetDevice, cudaChooseDevice,
cuPointerGetAttributes
Author
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