starpu-max/doc/doxygen/chapters/api/data_partition.doxy

/* StarPU --- Runtime system for heterogeneous multicore architectures.
 *
 * Copyright (C) 2010-2015,2017                           CNRS
 * Copyright (C) 2011-2013                                Inria
 * Copyright (C) 2009-2011,2014-2015,2017-2018            Université de Bordeaux
 *
 * StarPU is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at
 * your option) any later version.
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 * StarPU is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * See the GNU Lesser General Public License in COPYING.LGPL for more details.
 */

/*! \defgroup API_Data_Partition Data Partition

\struct starpu_data_filter
The filter structure describes a data partitioning operation, to be
given to the starpu_data_partition() function.
\ingroup API_Data_Partition
\var void (*starpu_data_filter::filter_func)(void *father_interface, void *child_interface, struct starpu_data_filter *filter, unsigned i, unsigned nparts)
    Fill the \p child_interface structure with interface information
    for the \p i -th child of the parent \p father_interface (among
    \p nparts). The \p filter structure is provided, allowing to inspect the
    starpu_data_filter::filter_arg and starpu_data_filter::filter_arg_ptr
    parameters.

    The details of what needs to be filled in \p child_interface vary according
    to the data interface, but generally speaking:
    <ul>
    <li> <c>id</c> is usually just copied over from the father, when the sub data has the same structure as the father, e.g. a subvector is a vector, a submatrix is a matrix, etc. This is however not the case for instance when dividing a BCSR matrix into its dense blocks, which then are matrices. </li>
    <li> <c>nx</c>, <c>ny</c> and alike are usually divided by the number of subdata, depending how the subdivision is done (e.g. nx division vs ny division for vertical matrix division vs horizontal matrix division). </li>
    <li> <c>ld</c> for matrix interfaces are usually just copied over: the leading dimension (ld) usually does not change. </li>
    <li> <c>elemsize</c> is usually just copied over. </li>
    <li> <c>ptr</c>, the pointer to the data, has to be computed according to \p i and the father's <c>ptr</c>, so as to point to the start of the sub data. This should however be done only if the father has <c>ptr</c> different from NULL: in the OpenCL case notably, the <c>dev_handle</c> and <c>offset</c> fields are used instead. </li>
    <li> <c>dev_handle</c> should be just copied over from the parent. </li>
    <li> <c>offset</c> has to be computed according to \p i and the father's <c>offset</c>, so as to provide the offset of the start of the sub data. This is notably used for the OpenCL case.
    </ul>
\var unsigned starpu_data_filter::nchildren
    Number of parts to partition the data into.
\var unsigned (*starpu_data_filter::get_nchildren)(struct starpu_data_filter *, starpu_data_handle_t initial_handle)
    Return the number of children. This can be used instead of
    starpu_data_filter::nchildren when the number of children depends
    on the actual data (e.g. the number of blocks in a sparse matrix).
\var struct starpu_data_interface_ops *(*starpu_data_filter::get_child_ops)(struct starpu_data_filter *, unsigned id)
    In case the resulting children use a different data interface,
    this function returns which interface is used by child number \p
    id.
\var unsigned starpu_data_filter::filter_arg
    Additional parameter for the filter function
\var void *starpu_data_filter::filter_arg_ptr
    Additional pointer parameter for the filter
    function, such as the sizes of the different parts.

@name Basic API
\ingroup API_Data_Partition

\fn void starpu_data_partition(starpu_data_handle_t initial_handle, struct starpu_data_filter *f)
\ingroup API_Data_Partition
Request the partitioning of \p initial_handle into several subdata
according to the filter \p f.

Here an example of how to use the function.
\code{.c}
struct starpu_data_filter f =
{
        .filter_func = starpu_matrix_filter_block,
        .nchildren = nslicesx
};
starpu_data_partition(A_handle, &f);
\endcode

\fn void starpu_data_unpartition(starpu_data_handle_t root_data, unsigned gathering_node)
\ingroup API_Data_Partition
Unapply the filter which has been applied to \p root_data, thus
unpartitioning the data. The pieces of data are collected back into
one big piece in the \p gathering_node (usually ::STARPU_MAIN_RAM).
Tasks working on the partitioned data must be already finished when
calling starpu_data_unpartition().

Here an example of how to use the function.
\code{.c}
starpu_data_unpartition(A_handle, STARPU_MAIN_RAM);
\endcode

\fn int starpu_data_get_nb_children(starpu_data_handle_t handle)
\ingroup API_Data_Partition
Return the number of children \p handle has been partitioned into.

\fn starpu_data_handle_t starpu_data_get_child(starpu_data_handle_t handle, unsigned i)
\ingroup API_Data_Partition
Return the \p i -th child of the given \p handle, which must have been
partitionned beforehand.

\fn starpu_data_handle_t starpu_data_get_sub_data(starpu_data_handle_t root_data, unsigned depth, ... )
\ingroup API_Data_Partition
After partitioning a StarPU data by applying a filter,
starpu_data_get_sub_data() can be used to get handles for each of the
data portions. \p root_data is the parent data that was partitioned.
\p depth is the number of filters to traverse (in case several filters
have been applied, to e.g. partition in row blocks, and then in column
blocks), and the subsequent parameters are the indexes. The function
returns a handle to the subdata.

Here an example of how to use the function.
\code{.c}
h = starpu_data_get_sub_data(A_handle, 1, taskx);
\endcode

\fn starpu_data_handle_t starpu_data_vget_sub_data(starpu_data_handle_t root_data, unsigned depth, va_list pa)
\ingroup API_Data_Partition
This function is similar to starpu_data_get_sub_data() but uses a
va_list for the parameter list.

\fn void starpu_data_map_filters(starpu_data_handle_t root_data, unsigned nfilters, ...)
\ingroup API_Data_Partition
Apply \p nfilters filters to the handle designated by
\p root_handle recursively. \p nfilters pointers to variables of the type
starpu_data_filter should be given.

\fn void starpu_data_vmap_filters(starpu_data_handle_t root_data, unsigned nfilters, va_list pa)
\ingroup API_Data_Partition
Apply \p nfilters filters to the handle designated by
\p root_handle recursively. It uses a va_list of pointers to variables of
the type starpu_data_filter.

@name Asynchronous API
\ingroup API_Data_Partition

\fn void starpu_data_partition_plan(starpu_data_handle_t initial_handle, struct starpu_data_filter *f, starpu_data_handle_t *children)
\ingroup API_Data_Partition
Plan to partition \p initial_handle into several subdata according to
the filter \p f.
The handles are returned into the \p children array, which has to be
the same size as the number of parts described in \p f. These handles
are not immediately usable, starpu_data_partition_submit() has to be
called to submit the actual partitioning.

Here is an example of how to use the function:

\code{.c}
starpu_data_handle_t children[nslicesx];
struct starpu_data_filter f =
{
        .filter_func = starpu_matrix_filter_block,
        .nchildren = nslicesx
};
starpu_data_partition_plan(A_handle, &f, children);
\endcode

\fn void starpu_data_partition_submit(starpu_data_handle_t initial_handle, unsigned nparts, starpu_data_handle_t *children)
\ingroup API_Data_Partition
Submit the actual partitioning of \p initial_handle into the \p nparts
\p children handles. This call is asynchronous, it only submits that the
partitioning should be done, so that the \p children handles can now be used to
submit tasks, and \p initial_handle can not be used to submit tasks any more (to
guarantee coherency).

For instance,

\code{.c}
starpu_data_partition_submit(A_handle, nslicesx, children);
\endcode

\fn void starpu_data_partition_readonly_submit(starpu_data_handle_t initial_handle, unsigned nparts, starpu_data_handle_t *children)
\ingroup API_Data_Partition
This is the same as starpu_data_partition_submit(), but it does not invalidate \p
initial_handle. This allows to continue using it, but the application has to be
careful not to write to \p initial_handle or \p children handles, only read from
them, since the coherency is otherwise not guaranteed.  This thus allows to
submit various tasks which concurrently read from various partitions of the data.

When the application wants to write to \p initial_handle again, it should call
starpu_data_unpartition_submit(), which will properly add dependencies between the
reads on the \p children and the writes to be submitted.

If instead the application wants to write to \p children handles, it should
call starpu_data_partition_readwrite_upgrade_submit(), which will correctly add
dependencies between the reads on the \p initial_handle and the writes to be
submitted.

\fn void starpu_data_partition_readwrite_upgrade_submit(starpu_data_handle_t initial_handle, unsigned nparts, starpu_data_handle_t *children)
\ingroup API_Data_Partition
This assumes that a partitioning of \p initial_handle has already been submited
in readonly mode through starpu_data_partition_readonly_submit(), and will upgrade
that partitioning into read-write mode for the \p children, by invalidating \p
initial_handle, and adding the necessary dependencies.

\fn void starpu_data_unpartition_submit(starpu_data_handle_t initial_handle, unsigned nparts, starpu_data_handle_t *children, int gathering_node)
\ingroup API_Data_Partition
This assumes that \p initial_handle is partitioned into \p children, and submits
an unpartitionning of it, i.e. submitting a gathering of the pieces on the
requested \p gathering_node memory node, and submitting an invalidation of the
children.

\p gathering_node can be set to -1 to let the runtime decide which memory node
should be used to gather the pieces.

This call is asynchronous, it only submits that the unpartitioning should be
done, so that the \p children handles should not be used to submit tasks any
more, and \p initial_handle can now be used again to submit tasks.

\fn void starpu_data_unpartition_readonly_submit(starpu_data_handle_t initial_handle, unsigned nparts, starpu_data_handle_t *children, int gathering_node)
\ingroup API_Data_Partition
This assumes that \p initial_handle is partitioned into \p children, and submits
just a readonly unpartitionning of it, i.e. submitting a gathering of the pieces
on the requested \p gathering_node memory node. It does not invalidate the
children. This brings \p initial_handle and \p children handles to the same
state as obtained with starpu_data_partition_readonly_submit().

\p gathering_node can be set to -1 to let the runtime decide which memory node
should be used to gather the pieces.

\fn void starpu_data_partition_clean(starpu_data_handle_t root_data, unsigned nparts, starpu_data_handle_t *children)
\ingroup API_Data_Partition
This should be used to clear the partition planning established between \p
root_data and \p children with starpu_data_partition_plan(). This will notably
submit an unregister all the \p children, which can thus not be used any more
afterwards.

@name Predefined Vector Filter Functions
\ingroup API_Data_Partition

This section gives a partial list of the predefined partitioning
functions for vector data. Examples on how to use them are shown in
\ref PartitioningData. The complete list can be found in the file
<c>starpu_data_filters.h</c>.

\fn void starpu_vector_filter_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Return in \p child_interface the \p id th element of the vector
represented by \p father_interface once partitioned in \p nparts chunks of
equal size.

\fn void starpu_vector_filter_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Return in \p child_interface the \p id th element of the vector
represented by \p father_interface once partitioned in \p nparts chunks of
equal size with a shadow border <c>filter_arg_ptr</c>, thus getting a vector
of size <c>(n-2*shadow)/nparts+2*shadow</c>. The <c>filter_arg_ptr</c> field
of \p f must be the shadow size casted into \c void*.

<b>IMPORTANT</b>: This can only be used for read-only access, as no coherency is
enforced for the shadowed parts. An usage example is available in
examples/filters/shadow.c

\fn void starpu_vector_filter_list_long(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Return in \p child_interface the \p id th element of the vector
represented by \p father_interface once partitioned into \p nparts chunks
according to the <c>filter_arg_ptr</c> field of \p f. The
<c>filter_arg_ptr</c> field must point to an array of \p nparts long
elements, each of which specifies the number of elements in each chunk
of the partition.

\fn void starpu_vector_filter_list(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Return in \p child_interface the \p id th element of the vector
represented by \p father_interface once partitioned into \p nparts chunks
according to the <c>filter_arg_ptr</c> field of \p f. The
<c>filter_arg_ptr</c> field must point to an array of \p nparts uint32_t
elements, each of which specifies the number of elements in each chunk
of the partition.

\fn void starpu_vector_filter_divide_in_2(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Return in \p child_interface the \p id th element of the vector
represented by \p father_interface once partitioned in <c>2</c> chunks of
equal size, ignoring nparts. Thus, \p id must be <c>0</c> or <c>1</c>.

@name Predefined Matrix Filter Functions
\ingroup API_Data_Partition

This section gives a partial list of the predefined partitioning
functions for matrix data. Examples on how to use them are shown in
\ref PartitioningData. The complete list can be found in the file
<c>starpu_data_filters.h</c>.

\fn void starpu_matrix_filter_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a dense Matrix along the x dimension, thus
getting (x/\p nparts ,y) matrices. If \p nparts does not divide x, the
last submatrix contains the remainder.

\fn void starpu_matrix_filter_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a dense Matrix along the x dimension, with a
shadow border <c>filter_arg_ptr</c>, thus getting ((x-2*shadow)/\p
nparts +2*shadow,y) matrices. If \p nparts does not divide x-2*shadow,
the last submatrix contains the remainder.

<b>IMPORTANT</b>: This can
only be used for read-only access, as no coherency is enforced for the
shadowed parts. A usage example is available in
examples/filters/shadow2d.c

\fn void starpu_matrix_filter_vertical_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a dense Matrix along the y dimension, thus
getting (x,y/\p nparts) matrices. If \p nparts does not divide y, the
last submatrix contains the remainder.

\fn void starpu_matrix_filter_vertical_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a dense Matrix along the y dimension, with a
shadow border <c>filter_arg_ptr</c>, thus getting
(x,(y-2*shadow)/\p nparts +2*shadow) matrices. If \p nparts does not
divide y-2*shadow, the last submatrix contains the remainder.

<b>IMPORTANT</b>: This can only be used for read-only access, as no
coherency is enforced for the shadowed parts. A usage example is
available in examples/filters/shadow2d.c

@name Predefined Block Filter Functions
\ingroup API_Data_Partition

This section gives a partial list of the predefined partitioning
functions for block data. Examples on how to use them are shown in
\ref PartitioningData. The complete list can be found in the file
<c>starpu_data_filters.h</c>. A usage example is available in
examples/filters/shadow3d.c

\fn void starpu_block_filter_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the X dimension, thus getting
(x/\p nparts ,y,z) 3D matrices. If \p nparts does not divide x, the last
submatrix contains the remainder.

\fn void starpu_block_filter_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the X dimension, with a
shadow border <c>filter_arg_ptr</c>, thus getting
((x-2*shadow)/\p nparts +2*shadow,y,z) blocks. If \p nparts does not
divide x, the last submatrix contains the remainder.

<b>IMPORTANT</b>:
This can only be used for read-only access, as no coherency is
enforced for the shadowed parts.

\fn void starpu_block_filter_vertical_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the Y dimension, thus getting
(x,y/\p nparts ,z) blocks. If \p nparts does not divide y, the last
submatrix contains the remainder.

\fn void starpu_block_filter_vertical_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the Y dimension, with a
shadow border <c>filter_arg_ptr</c>, thus getting
(x,(y-2*shadow)/\p nparts +2*shadow,z) 3D matrices. If \p nparts does not
divide y, the last submatrix contains the remainder.

<b>IMPORTANT</b>:
This can only be used for read-only access, as no coherency is
enforced for the shadowed parts.

\fn void starpu_block_filter_depth_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the Z dimension, thus getting
(x,y,z/\p nparts) blocks. If \p nparts does not divide z, the last
submatrix contains the remainder.

\fn void starpu_block_filter_depth_block_shadow(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block along the Z dimension, with a
shadow border <c>filter_arg_ptr</c>, thus getting
(x,y,(z-2*shadow)/\p nparts +2*shadow) blocks. If \p nparts does not
divide z, the last submatrix contains the remainder.

<b>IMPORTANT</b>:
This can only be used for read-only access, as no coherency is
enforced for the shadowed parts.

@name Predefined BCSR Filter Functions
\ingroup API_Data_Partition

This section gives a partial list of the predefined partitioning
functions for BCSR data. Examples on how to use them are shown in
\ref PartitioningData. The complete list can be found in the file
<c>starpu_data_filters.h</c>.

\fn void starpu_bcsr_filter_canonical_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block-sparse matrix into dense matrices.

\fn void starpu_csr_filter_vertical_block(void *father_interface, void *child_interface, struct starpu_data_filter *f, unsigned id, unsigned nparts)
\ingroup API_Data_Partition
Partition a block-sparse matrix into vertical block-sparse matrices.

*/