test/source/blender/blenlib/intern/task_range.cc

/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

/** \file
 * \ingroup bli
 *
 * Task parallel range functions.
 */

#include <cstdlib>

#include "MEM_guardedalloc.h"

#include "BLI_array.hh"
#include "BLI_lazy_threading.hh"
#include "BLI_offset_indices.hh"
#include "BLI_task.h"
#include "BLI_task.hh"
#include "BLI_threads.h"
#include "BLI_vector.hh"

#include "atomic_ops.h"

#ifdef WITH_TBB
#  include <tbb/blocked_range.h>
#  include <tbb/enumerable_thread_specific.h>
#  include <tbb/parallel_for.h>
#  include <tbb/parallel_reduce.h>
#endif

#ifdef WITH_TBB

/* Functor for running TBB parallel_for and parallel_reduce. */
struct RangeTask {
  TaskParallelRangeFunc func;
  void *userdata;
  const TaskParallelSettings *settings;

  void *userdata_chunk;

  /* Root constructor. */
  RangeTask(TaskParallelRangeFunc func, void *userdata, const TaskParallelSettings *settings)
      : func(func), userdata(userdata), settings(settings)
  {
    init_chunk(settings->userdata_chunk);
  }

  /* Copy constructor. */
  RangeTask(const RangeTask &other)
      : func(other.func), userdata(other.userdata), settings(other.settings)
  {
    init_chunk(settings->userdata_chunk);
  }

  /* Splitting constructor for parallel reduce. */
  RangeTask(RangeTask &other, tbb::split /*unused*/)
      : func(other.func), userdata(other.userdata), settings(other.settings)
  {
    init_chunk(settings->userdata_chunk);
  }

  ~RangeTask()
  {
    if (settings->func_free != nullptr) {
      settings->func_free(userdata, userdata_chunk);
    }
    MEM_SAFE_FREE(userdata_chunk);
  }

  void init_chunk(void *from_chunk)
  {
    if (from_chunk) {
      userdata_chunk = MEM_mallocN(settings->userdata_chunk_size, "RangeTask");
      memcpy(userdata_chunk, from_chunk, settings->userdata_chunk_size);
    }
    else {
      userdata_chunk = nullptr;
    }
  }

  void operator()(const tbb::blocked_range<int> &r) const
  {
    TaskParallelTLS tls;
    tls.userdata_chunk = userdata_chunk;
    for (int i = r.begin(); i != r.end(); ++i) {
      func(userdata, i, &tls);
    }
  }

  void join(const RangeTask &other)
  {
    settings->func_reduce(userdata, userdata_chunk, other.userdata_chunk);
  }
};

#endif

void BLI_task_parallel_range(const int start,
                             const int stop,
                             void *userdata,
                             TaskParallelRangeFunc func,
                             const TaskParallelSettings *settings)
{
#ifdef WITH_TBB
  /* Multithreading. */
  if (settings->use_threading && BLI_task_scheduler_num_threads() > 1) {
    RangeTask task(func, userdata, settings);
    const size_t grainsize = std::max(settings->min_iter_per_thread, 1);
    const tbb::blocked_range<int> range(start, stop, grainsize);

    blender::lazy_threading::send_hint();

    if (settings->func_reduce) {
      parallel_reduce(range, task);
      if (settings->userdata_chunk) {
        memcpy(settings->userdata_chunk, task.userdata_chunk, settings->userdata_chunk_size);
      }
    }
    else {
      parallel_for(range, task);
    }
    return;
  }
#endif

  /* Single threaded. Nothing to reduce as everything is accumulated into the
   * main userdata chunk directly. */
  TaskParallelTLS tls;
  tls.userdata_chunk = settings->userdata_chunk;
  for (int i = start; i < stop; i++) {
    func(userdata, i, &tls);
  }
  if (settings->func_free != nullptr) {
    settings->func_free(userdata, settings->userdata_chunk);
  }
}

int BLI_task_parallel_thread_id(const TaskParallelTLS * /*tls*/)
{
#ifdef WITH_TBB
  /* Get a unique thread ID for texture nodes. In the future we should get rid
   * of the thread ID and change texture evaluation to not require per-thread
   * storage that can't be efficiently allocated on the stack. */
  static tbb::enumerable_thread_specific<int> tbb_thread_id(-1);
  static int tbb_thread_id_counter = 0;

  int &thread_id = tbb_thread_id.local();
  if (thread_id == -1) {
    thread_id = atomic_fetch_and_add_int32(&tbb_thread_id_counter, 1);
    if (thread_id >= BLENDER_MAX_THREADS) {
      BLI_assert_msg(0, "Maximum number of threads exceeded for sculpting");
      thread_id = thread_id % BLENDER_MAX_THREADS;
    }
  }
  return thread_id;
#else
  return 0;
#endif
}

namespace blender::threading::detail {

void parallel_for_impl(const IndexRange range,
                       const int64_t grain_size,
                       const FunctionRef<void(IndexRange)> function)
{
#ifdef WITH_TBB
  /* Invoking tbb for small workloads has a large overhead. */
  if (range.size() >= grain_size) {
    lazy_threading::send_hint();
    tbb::parallel_for(
        tbb::blocked_range<int64_t>(range.first(), range.one_after_last(), grain_size),
        [function](const tbb::blocked_range<int64_t> &subrange) {
          function(IndexRange(subrange.begin(), subrange.size()));
        });
    return;
  }
#else
  UNUSED_VARS(grain_size);
#endif
  function(range);
}

void parallel_for_weighted_impl(
    const IndexRange range,
    const int64_t grain_size,
    const FunctionRef<void(IndexRange)> function,
    const FunctionRef<void(IndexRange, MutableSpan<int64_t>)> task_sizes_fn)
{
  /* Shouldn't be too small, because then there is more overhead when the individual tasks are
   * small. Also shouldn't be too large because then the serial code to split up tasks causes extra
   * overhead. */
  const int64_t outer_grain_size = std::min<int64_t>(grain_size, 512);
  threading::parallel_for(range, outer_grain_size, [&](const IndexRange sub_range) {
    /* Compute the size of every task in the current range. */
    Array<int64_t, 1024> task_sizes(sub_range.size());
    task_sizes_fn(sub_range, task_sizes);

    /* Split range into multiple segments that have a size that approximates the grain size. */
    Vector<int64_t, 256> offsets_vec;
    offsets_vec.append(0);
    int64_t counter = 0;
    for (const int64_t i : sub_range.index_range()) {
      counter += task_sizes[i];
      if (counter >= grain_size) {
        offsets_vec.append(i + 1);
        counter = 0;
      }
    }
    if (offsets_vec.last() < sub_range.size()) {
      offsets_vec.append(sub_range.size());
    }
    const OffsetIndices<int64_t> offsets = offsets_vec.as_span();

    /* Run the dynamically split tasks in parallel. */
    threading::parallel_for(offsets.index_range(), 1, [&](const IndexRange offsets_range) {
      for (const int64_t i : offsets_range) {
        const IndexRange actual_range = offsets[i].shift(sub_range.start());
        function(actual_range);
      }
    });
  });
}

void memory_bandwidth_bound_task_impl(const FunctionRef<void()> function)
{
#ifdef WITH_TBB
  /* This is the maximum number of threads that may perform these memory bandwidth bound tasks at
   * the same time. Often fewer threads are already enough to use up the full bandwidth capacity.
   * Additional threads usually have a negilible benefit and can even make performance worse.
   *
   * It's better to use fewer threads here so that the CPU cores can do other tasks at the same
   * time which may be more compute intensive. */
  const int num_threads = 8;
  if (num_threads >= BLI_task_scheduler_num_threads()) {
    /* Avoid overhead of using a task arena when it would not have any effect anyway. */
    function();
    return;
  }
  static tbb::task_arena arena{num_threads};

  /* Make sure the lazy threading hints are send now, because they shouldn't be send out of an
   * isolated region. */
  lazy_threading::send_hint();
  lazy_threading::ReceiverIsolation isolation;

  arena.execute(function);
#else
  function();
#endif
}

}  // namespace blender::threading::detail