Detailed description

template< typename InputT, int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>
class cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >

The BlockExchange class provides collective methods for rearranging data partitioned across a CUDA thread block.

.

Template Parameters

T	The data type to be exchanged.
BLOCK_DIM_X	The thread block length in threads along the X dimension
ITEMS_PER_THREAD	The number of items partitioned onto each thread.
WARP_TIME_SLICING	[optional] When `true`, only use enough shared memory for a single warp's worth of tile data, time-slicing the block-wide exchange over multiple synchronized rounds. Yields a smaller memory footprint at the expense of decreased parallelism. (Default: false)
BLOCK_DIM_Y	[optional] The thread block length in threads along the Y dimension (default: 1)
BLOCK_DIM_Z	[optional] The thread block length in threads along the Z dimension (default: 1)
PTX_ARCH	[optional] The PTX compute capability for which to to specialize this collective, formatted as per the `CUDA_ARCH` macro (e.g., 350 for sm_35). Useful for determining the collective's storage requirements for a given device from the host. (Default: the value of `CUDA_ARCH` during the current compiler pass)

Overview

It is commonplace for blocks of threads to rearrange data items between threads. For example, the device-accessible memory subsystem prefers access patterns where data items are "striped" across threads (where consecutive threads access consecutive items), yet most block-wide operations prefer a "blocked" partitioning of items across threads (where consecutive items belong to a single thread).
BlockExchange supports the following types of data exchanges:
- Transposing between blocked and striped arrangements
- Transposing between blocked and warp-striped arrangements
- Scattering ranked items to a blocked arrangement
- Scattering ranked items to a striped arrangement
For multi-dimensional blocks, threads are linearly ranked in row-major order.

A Simple Example: Every thread in the block uses the BlockExchange class by first specializing the BlockExchange type, then instantiating an instance with parameters for communication, and finally invoking one or more collective member functions.

: The code snippet below illustrates the conversion from a "blocked" to a "striped" arrangement of 512 integer items partitioned across 128 threads where each thread owns 4 items.

: #include <cub/cub.cuh> // or equivalently <cub/block/block_exchange.cuh>

__global__ void ExampleKernel(int *d_data, ...)

{

// Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each

typedef cub::BlockExchange<int, 128, 4> BlockExchange;

// Allocate shared memory for BlockExchange

__shared__ typename BlockExchange::TempStorage temp_storage;

// Load a tile of data striped across threads

int thread_data[4];

cub::LoadDirectStriped<128>(threadIdx.x, d_data, thread_data);

// Collectively exchange data into a blocked arrangement across threads

BlockExchange(temp_storage).StripedToBlocked(thread_data);

: Suppose the set of striped input thread_data across the block of threads is { [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] }. The corresponding output thread_data in those threads will be { [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }.

Performance Considerations

Proper device-specific padding ensures zero bank conflicts for most types.

Re-using dynamically allocating shared memory: The following example under the examples/block folder illustrates usage of dynamically shared memory with BlockReduce and how to re-purpose the same memory region: example_block_reduce_dyn_smem.cu

This example can be easily adapted to the storage required by BlockExchange.

Classes
struct	TempStorage
	The operations exposed by BlockExchange require a temporary memory allocation of this nested type for thread communication. This opaque storage can be allocated directly using the `__shared__` keyword. Alternatively, it can be aliased to externally allocated memory (shared or global) or `union`'d with other storage allocation types to facilitate memory reuse. More...

Public Methods
Collective constructors
__device__ __forceinline__	BlockExchange ()
	Collective constructor using a private static allocation of shared memory as temporary storage. More...

__device__ __forceinline__	BlockExchange (TempStorage &temp_storage)
	Collective constructor using the specified memory allocation as temporary storage. More...

Structured exchanges
template<typename OutputT >
__device__ __forceinline__ void	StripedToBlocked (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD])
	Transposes data items from striped arrangement to blocked arrangement. More...

template<typename OutputT >
__device__ __forceinline__ void	BlockedToStriped (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD])
	Transposes data items from blocked arrangement to striped arrangement. More...

template<typename OutputT >
__device__ __forceinline__ void	WarpStripedToBlocked (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD])
	Transposes data items from warp-striped arrangement to blocked arrangement. More...

template<typename OutputT >
__device__ __forceinline__ void	BlockedToWarpStriped (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD])
	Transposes data items from blocked arrangement to warp-striped arrangement. More...

Scatter exchanges
template<typename OutputT , typename OffsetT >
__device__ __forceinline__ void	ScatterToBlocked (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD], OffsetT(&ranks)[ITEMS_PER_THREAD])
	Exchanges data items annotated by rank into blocked arrangement. More...

template<typename OutputT , typename OffsetT >
__device__ __forceinline__ void	ScatterToStriped (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD], OffsetT(&ranks)[ITEMS_PER_THREAD])
	Exchanges data items annotated by rank into striped arrangement. More...

template<typename OutputT , typename OffsetT >
__device__ __forceinline__ void	ScatterToStripedGuarded (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD], OffsetT(&ranks)[ITEMS_PER_THREAD])
	Exchanges data items annotated by rank into striped arrangement. Items with rank -1 are not exchanged. More...

template<typename OutputT , typename OffsetT , typename ValidFlag >
__device__ __forceinline__ void	ScatterToStripedFlagged (InputT(&input_items)[ITEMS_PER_THREAD], OutputT(&output_items)[ITEMS_PER_THREAD], OffsetT(&ranks)[ITEMS_PER_THREAD], ValidFlag(&is_valid)[ITEMS_PER_THREAD])
	Exchanges valid data items annotated by rank into striped arrangement. More...

Constructor & Destructor Documentation

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

__device__ __forceinline__ cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::BlockExchange ( )

inline

Collective constructor using a private static allocation of shared memory as temporary storage.

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

__device__ __forceinline__ cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::BlockExchange ( TempStorage & temp_storage)

inline

Collective constructor using the specified memory allocation as temporary storage.

Parameters

[in] temp_storage Reference to memory allocation having layout type TempStorage

Member Function Documentation

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::StripedToBlocked	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD]
	)

inline

Transposes data items from striped arrangement to blocked arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Snippet: The code snippet below illustrates the conversion from a "striped" to a "blocked" arrangement of 512 integer items partitioned across 128 threads where each thread owns 4 items.

: #include <cub/cub.cuh> // or equivalently <cub/block/block_exchange.cuh>

__global__ void ExampleKernel(int *d_data, ...)

{

// Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each

typedef cub::BlockExchange<int, 128, 4> BlockExchange;

// Allocate shared memory for BlockExchange

__shared__ typename BlockExchange::TempStorage temp_storage;

// Load a tile of ordered data into a striped arrangement across block threads

int thread_data[4];

cub::LoadDirectStriped<128>(threadIdx.x, d_data, thread_data);

// Collectively exchange data into a blocked arrangement across threads

BlockExchange(temp_storage).StripedToBlocked(thread_data, thread_data);

: Suppose the set of striped input thread_data across the block of threads is { [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] } after loading from device-accessible memory. The corresponding output thread_data in those threads will be { [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }.

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::BlockedToStriped	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD]
	)

inline

Transposes data items from blocked arrangement to striped arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Snippet: The code snippet below illustrates the conversion from a "blocked" to a "striped" arrangement of 512 integer items partitioned across 128 threads where each thread owns 4 items.

: #include <cub/cub.cuh> // or equivalently <cub/block/block_exchange.cuh>

__global__ void ExampleKernel(int *d_data, ...)

{

// Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each

typedef cub::BlockExchange<int, 128, 4> BlockExchange;

// Allocate shared memory for BlockExchange

__shared__ typename BlockExchange::TempStorage temp_storage;

// Obtain a segment of consecutive items that are blocked across threads

int thread_data[4];

...

// Collectively exchange data into a striped arrangement across threads

BlockExchange(temp_storage).BlockedToStriped(thread_data, thread_data);

// Store data striped across block threads into an ordered tile

cub::StoreDirectStriped<STORE_DEFAULT, 128>(threadIdx.x, d_data, thread_data);

: Suppose the set of blocked input thread_data across the block of threads is { [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }. The corresponding output thread_data in those threads will be { [0,128,256,384], [1,129,257,385], ..., [127,255,383,511] } in preparation for storing to device-accessible memory.

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::WarpStripedToBlocked	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD]
	)

inline

Transposes data items from warp-striped arrangement to blocked arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Snippet: The code snippet below illustrates the conversion from a "warp-striped" to a "blocked" arrangement of 512 integer items partitioned across 128 threads where each thread owns 4 items.

: #include <cub/cub.cuh> // or equivalently <cub/block/block_exchange.cuh>

__global__ void ExampleKernel(int *d_data, ...)

{

// Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each

typedef cub::BlockExchange<int, 128, 4> BlockExchange;

// Allocate shared memory for BlockExchange

__shared__ typename BlockExchange::TempStorage temp_storage;

// Load a tile of ordered data into a warp-striped arrangement across warp threads

int thread_data[4];

cub::LoadSWarptriped<LOAD_DEFAULT>(threadIdx.x, d_data, thread_data);

// Collectively exchange data into a blocked arrangement across threads

BlockExchange(temp_storage).WarpStripedToBlocked(thread_data);

: Suppose the set of warp-striped input thread_data across the block of threads is { [0,32,64,96], [1,33,65,97], [2,34,66,98], ..., [415,447,479,511] } after loading from device-accessible memory. (The first 128 items are striped across the first warp of 32 threads, the second 128 items are striped across the second warp, etc.) The corresponding output thread_data in those threads will be { [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }.

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::BlockedToWarpStriped	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD]
	)

inline

Transposes data items from blocked arrangement to warp-striped arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Snippet: The code snippet below illustrates the conversion from a "blocked" to a "warp-striped" arrangement of 512 integer items partitioned across 128 threads where each thread owns 4 items.

: #include <cub/cub.cuh> // or equivalently <cub/block/block_exchange.cuh>

__global__ void ExampleKernel(int *d_data, ...)

{

// Specialize BlockExchange for a 1D block of 128 threads owning 4 integer items each

typedef cub::BlockExchange<int, 128, 4> BlockExchange;

// Allocate shared memory for BlockExchange

__shared__ typename BlockExchange::TempStorage temp_storage;

// Obtain a segment of consecutive items that are blocked across threads

int thread_data[4];

...

// Collectively exchange data into a warp-striped arrangement across threads

BlockExchange(temp_storage).BlockedToWarpStriped(thread_data, thread_data);

// Store data striped across warp threads into an ordered tile

cub::StoreDirectStriped<STORE_DEFAULT, 128>(threadIdx.x, d_data, thread_data);

: Suppose the set of blocked input thread_data across the block of threads is { [0,1,2,3], [4,5,6,7], [8,9,10,11], ..., [508,509,510,511] }. The corresponding output thread_data in those threads will be { [0,32,64,96], [1,33,65,97], [2,34,66,98], ..., [415,447,479,511] } in preparation for storing to device-accessible memory. (The first 128 items are striped across the first warp of 32 threads, the second 128 items are striped across the second warp, etc.)

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT , typename OffsetT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::ScatterToBlocked	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD],
		OffsetT(&)	ranks[ITEMS_PER_THREAD]
	)

inline

Exchanges data items annotated by rank into blocked arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Template Parameters

OffsetT [inferred] Signed integer type for local offsets

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.
[in]	ranks	Corresponding scatter ranks

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT , typename OffsetT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::ScatterToStriped	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD],
		OffsetT(&)	ranks[ITEMS_PER_THREAD]
	)

inline

Exchanges data items annotated by rank into striped arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Template Parameters

OffsetT [inferred] Signed integer type for local offsets

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.
[in]	ranks	Corresponding scatter ranks

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT , typename OffsetT >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::ScatterToStripedGuarded	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD],
		OffsetT(&)	ranks[ITEMS_PER_THREAD]
	)

inline

Exchanges data items annotated by rank into striped arrangement. Items with rank -1 are not exchanged.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Template Parameters

OffsetT [inferred] Signed integer type for local offsets

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.
[in]	ranks	Corresponding scatter ranks

template<typename InputT , int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>

template<typename OutputT , typename OffsetT , typename ValidFlag >

__device__ __forceinline__ void cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >::ScatterToStripedFlagged	(	InputT(&)	input_items[ITEMS_PER_THREAD],
		OutputT(&)	output_items[ITEMS_PER_THREAD],
		OffsetT(&)	ranks[ITEMS_PER_THREAD],
		ValidFlag(&)	is_valid[ITEMS_PER_THREAD]
	)

inline

Exchanges valid data items annotated by rank into striped arrangement.

A subsequent __syncthreads() threadblock barrier should be invoked after calling this method if the collective's temporary storage (e.g., temp_storage) is to be reused or repurposed.

Template Parameters

OffsetT	[inferred] Signed integer type for local offsets
ValidFlag	[inferred] FlagT type denoting which items are valid

Parameters

[in]	input_items	Items to exchange, converting between striped and blocked arrangements.
[out]	output_items	Items from exchange, converting between striped and blocked arrangements.
[in]	ranks	Corresponding scatter ranks
[in]	is_valid	Corresponding flag denoting item validity

The documentation for this class was generated from the following file:

block_exchange.cuh

Detailed description

template< typename InputT, int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH> class cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >

Classes

Public Methods

Constructor & Destructor Documentation

Member Function Documentation

template< typename InputT, int BLOCK_DIM_X, int ITEMS_PER_THREAD, bool WARP_TIME_SLICING = false, int BLOCK_DIM_Y = 1, int BLOCK_DIM_Z = 1, int PTX_ARCH = CUB_PTX_ARCH>
class cub::BlockExchange< InputT, BLOCK_DIM_X, ITEMS_PER_THREAD, WARP_TIME_SLICING, BLOCK_DIM_Y, BLOCK_DIM_Z, PTX_ARCH >