/// Maps the buffer into the host address space.
///
/// \see_opencl_ref{clEnqueueMapBuffer}
void map(cl_map_flags flags, command_queue &queue)
{
BOOST_ASSERT(m_mapped_ptr == 0);
m_mapped_ptr = queue.enqueue_map_buffer(
m_buffer, flags, 0, m_buffer.size()
);
}
inline DeviceIterator copy_to_device_map(HostIterator first,
HostIterator last,
DeviceIterator result,
command_queue &queue,
const wait_list &events)
{
typedef typename
std::iterator_traits<DeviceIterator>::value_type
value_type;
typedef typename
std::iterator_traits<DeviceIterator>::difference_type
difference_type;
size_t count = iterator_range_size(first, last);
if(count == 0){
return result;
}
size_t offset = result.get_index();
// map result buffer to host
value_type *pointer = static_cast<value_type*>(
queue.enqueue_map_buffer(
result.get_buffer(),
CL_MAP_WRITE,
offset * sizeof(value_type),
count * sizeof(value_type),
events
)
);
// copy [first; last) to result buffer
std::copy(first, last, pointer);
// unmap result buffer
boost::compute::event unmap_event = queue.enqueue_unmap_buffer(
result.get_buffer(),
static_cast<void*>(pointer)
);
unmap_event.wait();
return result + static_cast<difference_type>(count);
}
InputIterator find_extrema_with_reduce(InputIterator first,
InputIterator last,
::boost::compute::less<
typename std::iterator_traits<
InputIterator
>::value_type
>
compare,
const bool find_minimum,
command_queue &queue)
{
typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
typedef typename std::iterator_traits<InputIterator>::value_type input_type;
const context &context = queue.get_context();
const device &device = queue.get_device();
// Getting information about used queue and device
const size_t compute_units_no = device.get_info<CL_DEVICE_MAX_COMPUTE_UNITS>();
const size_t max_work_group_size = device.get_info<CL_DEVICE_MAX_WORK_GROUP_SIZE>();
const size_t count = detail::iterator_range_size(first, last);
std::string cache_key = std::string("__boost_find_extrema_with_reduce_")
+ type_name<input_type>();
// load parameters
boost::shared_ptr<parameter_cache> parameters =
detail::parameter_cache::get_global_cache(device);
// get preferred work group size and preferred number
// of work groups per compute unit
size_t work_group_size = parameters->get(cache_key, "wgsize", 256);
size_t work_groups_per_cu = parameters->get(cache_key, "wgpcu", 64);
// calculate work group size and number of work groups
work_group_size = (std::min)(max_work_group_size, work_group_size);
size_t work_groups_no = compute_units_no * work_groups_per_cu;
work_groups_no = (std::min)(
work_groups_no,
static_cast<size_t>(std::ceil(float(count) / work_group_size))
);
// phase I: finding candidates for extremum
// device buffors for extremum candidates and their indices
// each work-group computes its candidate
// zero-copy buffers are used to eliminate copying data back to host
vector<input_type, ::boost::compute::pinned_allocator<input_type> >
candidates(work_groups_no, context);
vector<uint_, ::boost::compute::pinned_allocator <uint_> >
candidates_idx(work_groups_no, context);
// finding candidates for first extremum and their indices
find_extrema_with_reduce(
first, count, candidates.begin(), candidates_idx.begin(),
work_groups_no, work_group_size, compare, find_minimum, queue
);
// phase II: finding extremum from among the candidates
// mapping candidates and their indices to host
input_type* candidates_host_ptr =
static_cast<input_type*>(
queue.enqueue_map_buffer(
candidates.get_buffer(), command_queue::map_read,
0, work_groups_no * sizeof(input_type)
)
);
uint_* candidates_idx_host_ptr =
static_cast<uint_*>(
queue.enqueue_map_buffer(
candidates_idx.get_buffer(), command_queue::map_read,
0, work_groups_no * sizeof(uint_)
)
);
input_type* i = candidates_host_ptr;
uint_* idx = candidates_idx_host_ptr;
uint_* extremum_idx = idx;
input_type extremum = *candidates_host_ptr;
i++; idx++;
// find extremum (serial) from among the candidates on host
if(!find_minimum) {
while(idx != (candidates_idx_host_ptr + work_groups_no)) {
input_type next = *i;
bool compare_result = next > extremum;
bool equal = next == extremum;
extremum = compare_result ? next : extremum;
extremum_idx = compare_result ? idx : extremum_idx;
extremum_idx = equal ? ((*extremum_idx < *idx) ? extremum_idx : idx) : extremum_idx;
idx++, i++;
}
}
else {
while(idx != (candidates_idx_host_ptr + work_groups_no)) {
input_type next = *i;
bool compare_result = next < extremum;
bool equal = next == extremum;
extremum = compare_result ? next : extremum;
extremum_idx = compare_result ? idx : extremum_idx;
extremum_idx = equal ? ((*extremum_idx < *idx) ? extremum_idx : idx) : extremum_idx;
idx++, i++;
}
}
return first + static_cast<difference_type>(*extremum_idx);
}
InputIterator find_extrema_with_reduce(InputIterator first,
InputIterator last,
Compare compare,
const bool find_minimum,
command_queue &queue)
{
typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
typedef typename std::iterator_traits<InputIterator>::value_type input_type;
const context &context = queue.get_context();
const device &device = queue.get_device();
// Getting information about used queue and device
const size_t compute_units_no = device.get_info<CL_DEVICE_MAX_COMPUTE_UNITS>();
const size_t max_work_group_size = device.get_info<CL_DEVICE_MAX_WORK_GROUP_SIZE>();
const size_t count = detail::iterator_range_size(first, last);
std::string cache_key = std::string("__boost_find_extrema_with_reduce_")
+ type_name<input_type>();
// load parameters
boost::shared_ptr<parameter_cache> parameters =
detail::parameter_cache::get_global_cache(device);
// get preferred work group size and preferred number
// of work groups per compute unit
size_t work_group_size = parameters->get(cache_key, "wgsize", 256);
size_t work_groups_per_cu = parameters->get(cache_key, "wgpcu", 100);
// calculate work group size and number of work groups
work_group_size = (std::min)(max_work_group_size, work_group_size);
size_t work_groups_no = compute_units_no * work_groups_per_cu;
work_groups_no = (std::min)(
work_groups_no,
static_cast<size_t>(std::ceil(float(count) / work_group_size))
);
// phase I: finding candidates for extremum
// device buffors for extremum candidates and their indices
// each work-group computes its candidate
vector<input_type> candidates(work_groups_no, context);
vector<uint_> candidates_idx(work_groups_no, context);
// finding candidates for first extremum and their indices
find_extrema_with_reduce(
first, count, candidates.begin(), candidates_idx.begin(),
work_groups_no, work_group_size, compare, find_minimum, queue
);
// phase II: finding extremum from among the candidates
// zero-copy buffers for final result (value and index)
vector<input_type, ::boost::compute::pinned_allocator<input_type> >
result(1, context);
vector<uint_, ::boost::compute::pinned_allocator<uint_> >
result_idx(1, context);
// get extremum from among the candidates
find_extrema_with_reduce(
candidates.begin(), candidates_idx.begin(), work_groups_no, result.begin(),
result_idx.begin(), 1, work_group_size, compare, find_minimum, true, queue
);
// mapping extremum index to host
uint_* result_idx_host_ptr =
static_cast<uint_*>(
queue.enqueue_map_buffer(
result_idx.get_buffer(), command_queue::map_read,
0, sizeof(uint_)
)
);
return first + static_cast<difference_type>(*result_idx_host_ptr);
}
inline InputIterator find_extrema_on_cpu(InputIterator first,
InputIterator last,
Compare compare,
const bool find_minimum,
command_queue &queue)
{
typedef typename std::iterator_traits<InputIterator>::value_type input_type;
typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
size_t count = iterator_range_size(first, last);
const device &device = queue.get_device();
const uint_ compute_units = queue.get_device().compute_units();
boost::shared_ptr<parameter_cache> parameters =
detail::parameter_cache::get_global_cache(device);
std::string cache_key =
"__boost_find_extrema_cpu_"
+ boost::lexical_cast<std::string>(sizeof(input_type));
// for inputs smaller than serial_find_extrema_threshold
// serial_find_extrema algorithm is used
uint_ serial_find_extrema_threshold = parameters->get(
cache_key,
"serial_find_extrema_threshold",
16384 * sizeof(input_type)
);
serial_find_extrema_threshold =
(std::max)(serial_find_extrema_threshold, uint_(2 * compute_units));
const context &context = queue.get_context();
if(count < serial_find_extrema_threshold) {
return serial_find_extrema(first, last, compare, find_minimum, queue);
}
meta_kernel k("find_extrema_on_cpu");
buffer output(context, sizeof(input_type) * compute_units);
buffer output_idx(
context, sizeof(uint_) * compute_units,
buffer::read_write | buffer::alloc_host_ptr
);
size_t count_arg = k.add_arg<uint_>("count");
size_t output_arg =
k.add_arg<input_type *>(memory_object::global_memory, "output");
size_t output_idx_arg =
k.add_arg<uint_ *>(memory_object::global_memory, "output_idx");
k <<
"uint block = " <<
"(uint)ceil(((float)count)/get_global_size(0));\n" <<
"uint index = get_global_id(0) * block;\n" <<
"uint end = min(count, index + block);\n" <<
"uint value_index = index;\n" <<
k.decl<input_type>("value") << " = " << first[k.var<uint_>("index")] << ";\n" <<
"index++;\n" <<
"while(index < end){\n" <<
k.decl<input_type>("candidate") <<
" = " << first[k.var<uint_>("index")] << ";\n" <<
"#ifndef BOOST_COMPUTE_FIND_MAXIMUM\n" <<
"bool compare = " << compare(k.var<input_type>("candidate"),
k.var<input_type>("value")) << ";\n" <<
"#else\n" <<
"bool compare = " << compare(k.var<input_type>("value"),
k.var<input_type>("candidate")) << ";\n" <<
"#endif\n" <<
"value = compare ? candidate : value;\n" <<
"value_index = compare ? index : value_index;\n" <<
"index++;\n" <<
"}\n" <<
"output[get_global_id(0)] = value;\n" <<
"output_idx[get_global_id(0)] = value_index;\n";
size_t global_work_size = compute_units;
std::string options;
if(!find_minimum){
options = "-DBOOST_COMPUTE_FIND_MAXIMUM";
}
kernel kernel = k.compile(context, options);
kernel.set_arg(count_arg, static_cast<uint_>(count));
kernel.set_arg(output_arg, output);
kernel.set_arg(output_idx_arg, output_idx);
queue.enqueue_1d_range_kernel(kernel, 0, global_work_size, 0);
buffer_iterator<input_type> result = serial_find_extrema(
make_buffer_iterator<input_type>(output),
make_buffer_iterator<input_type>(output, global_work_size),
compare,
find_minimum,
queue
);
uint_* output_idx_host_ptr =
static_cast<uint_*>(
queue.enqueue_map_buffer(
output_idx, command_queue::map_read,
0, global_work_size * sizeof(uint_)
)
);
difference_type extremum_idx =
static_cast<difference_type>(*(output_idx_host_ptr + result.get_index()));
return first + extremum_idx;
}