scheduler.c 49.8 KB
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/*******************************************************************************
 * This file is part of SWIFT.
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 * Copyright (c) 2012 Pedro Gonnet (pedro.gonnet@durham.ac.uk)
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 *                    Matthieu Schaller (matthieu.schaller@durham.ac.uk)
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 *               2016 Peter W. Draper (p.w.draper@durham.ac.uk)
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 *
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 * This program 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 3 of the License, or
 * (at your option) any later version.
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 *
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 * This program 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 General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
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 *
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 ******************************************************************************/

/* Config parameters. */
#include "../config.h"

/* Some standard headers. */
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#include <limits.h>
#include <math.h>
#include <pthread.h>
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

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/* MPI headers. */
#ifdef WITH_MPI
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#include <mpi.h>
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#endif

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/* This object's header. */
#include "scheduler.h"

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/* Local headers. */
#include "atomic.h"
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#include "cycle.h"
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#include "engine.h"
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#include "error.h"
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#include "intrinsics.h"
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#include "kernel_hydro.h"
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#include "queue.h"
#include "space.h"
#include "task.h"
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#include "timers.h"
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/**
 * @brief Re-set the list of active tasks.
 */
void scheduler_clear_active(struct scheduler *s) { s->active_count = 0; }

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/**
 * @brief Add an unlock_task to the given task.
 *
 * @param s The #scheduler.
 * @param ta The unlocking #task.
 * @param tb The #task that will be unlocked.
 */
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void scheduler_addunlock(struct scheduler *s, struct task *ta,
                         struct task *tb) {
  /* Get an index at which to store this unlock. */
  const int ind = atomic_inc(&s->nr_unlocks);

  /* Does the buffer need to be grown? */
  if (ind == s->size_unlocks) {
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    /* Allocate the new buffer. */
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    struct task **unlocks_new;
    int *unlock_ind_new;
    const int size_unlocks_new = s->size_unlocks * 2;
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    if ((unlocks_new = (struct task **)malloc(sizeof(struct task *) *
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                                              size_unlocks_new)) == NULL ||
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        (unlock_ind_new = (int *)malloc(sizeof(int) * size_unlocks_new)) ==
            NULL)
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      error("Failed to re-allocate unlocks.");
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    /* Wait for all writes to the old buffer to complete. */
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    while (s->completed_unlock_writes < ind)
      ;

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    /* Copy the buffers. */
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    memcpy(unlocks_new, s->unlocks, sizeof(struct task *) * ind);
    memcpy(unlock_ind_new, s->unlock_ind, sizeof(int) * ind);
    free(s->unlocks);
    free(s->unlock_ind);
    s->unlocks = unlocks_new;
    s->unlock_ind = unlock_ind_new;
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    /* Publish the new buffer size. */
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    s->size_unlocks = size_unlocks_new;
  }
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  /* Wait for there to actually be space at my index. */
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  while (ind > s->size_unlocks)
    ;
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  /* Write the unlock to the scheduler. */
  s->unlocks[ind] = tb;
  s->unlock_ind[ind] = ta - s->tasks;
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  atomic_inc(&s->completed_unlock_writes);
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}

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/**
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 * @brief Split a task if too large.
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 *
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 * @param t The #task
 * @param s The #scheduler we are working in.
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 */
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static void scheduler_splittask(struct task *t, struct scheduler *s) {
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  /* Static constants. */
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  static const int pts[7][8] = {
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      {-1, 12, 10, 9, 4, 3, 1, 0},     {-1, -1, 11, 10, 5, 4, 2, 1},
      {-1, -1, -1, 12, 7, 6, 4, 3},    {-1, -1, -1, -1, 8, 7, 5, 4},
      {-1, -1, -1, -1, -1, 12, 10, 9}, {-1, -1, -1, -1, -1, -1, 11, 10},
      {-1, -1, -1, -1, -1, -1, -1, 12}};
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  static const float sid_scale[13] = {
      0.1897f, 0.4025f, 0.1897f, 0.4025f, 0.5788f, 0.4025f, 0.1897f,
      0.4025f, 0.1897f, 0.4025f, 0.5788f, 0.4025f, 0.5788f};
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  /* Iterate on this task until we're done with it. */
  int redo = 1;
  while (redo) {
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    /* Reset the redo flag. */
    redo = 0;
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    /* Non-splittable task? */
    if ((t->ci == NULL || (t->type == task_type_pair && t->cj == NULL)) ||
        ((t->type == task_type_kick) && t->ci->nodeID != s->nodeID) ||
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        ((t->type == task_type_drift) && t->ci->nodeID != s->nodeID) ||
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        ((t->type == task_type_init) && t->ci->nodeID != s->nodeID)) {
      t->type = task_type_none;
      t->skip = 1;
      break;
    }
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    /* Self-interaction? */
    if (t->type == task_type_self) {
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      /* Get a handle on the cell involved. */
      struct cell *ci = t->ci;
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      const double hi = ci->dmin;
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      /* Foreign task? */
      if (ci->nodeID != s->nodeID) {
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        t->skip = 1;
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        break;
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      }

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      /* Is this cell even split? */
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      if (ci->split && ci->h_max * kernel_gamma * space_stretch < hi / 2) {
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        /* Make a sub? */
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        if (scheduler_dosub &&
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            ((ci->count > 0 && ci->count < space_subsize / ci->count) ||
             (ci->gcount > 0 && ci->gcount < space_subsize / ci->gcount))) {
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          /* convert to a self-subtask. */
          t->type = task_type_sub_self;

          /* Otherwise, make tasks explicitly. */
        } else {
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          /* Take a step back (we're going to recycle the current task)... */
          redo = 1;

          /* Add the self tasks. */
          int first_child = 0;
          while (ci->progeny[first_child] == NULL) first_child++;
          t->ci = ci->progeny[first_child];
          for (int k = first_child + 1; k < 8; k++)
            if (ci->progeny[k] != NULL)
              scheduler_splittask(
                  scheduler_addtask(s, task_type_self, t->subtype, 0, 0,
                                    ci->progeny[k], NULL, 0),
                  s);

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          /* Make a task for each pair of progeny unless it's ext. gravity. */
          if (t->subtype != task_subtype_external_grav) {

            for (int j = 0; j < 8; j++)
              if (ci->progeny[j] != NULL)
                for (int k = j + 1; k < 8; k++)
                  if (ci->progeny[k] != NULL)
                    scheduler_splittask(
                        scheduler_addtask(s, task_type_pair, t->subtype,
                                          pts[j][k], 0, ci->progeny[j],
                                          ci->progeny[k], 0),
                        s);
          }
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        }
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      }
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      /* Pair interaction? */
    } else if (t->type == task_type_pair && t->subtype != task_subtype_grav) {
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      /* Get a handle on the cells involved. */
      struct cell *ci = t->ci;
      struct cell *cj = t->cj;
      const double hi = ci->dmin;
      const double hj = cj->dmin;
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      /* Foreign task? */
      if (ci->nodeID != s->nodeID && cj->nodeID != s->nodeID) {
        t->skip = 1;
        break;
      }
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      /* Get the sort ID, use space_getsid and not t->flags
         to make sure we get ci and cj swapped if needed. */
      double shift[3];
      int sid = space_getsid(s->space, &ci, &cj, shift);
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      /* Should this task be split-up? */
      if (ci->split && cj->split &&
          ci->h_max * kernel_gamma * space_stretch < hi / 2 &&
          cj->h_max * kernel_gamma * space_stretch < hj / 2) {

        /* Replace by a single sub-task? */
        if (scheduler_dosub &&
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            ci->count * sid_scale[sid] < space_subsize / cj->count &&
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            sid != 0 && sid != 2 && sid != 6 && sid != 8) {

          /* Make this task a sub task. */
          t->type = task_type_sub_pair;

          /* Otherwise, split it. */
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        } else {

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          /* Take a step back (we're going to recycle the current task)... */
          redo = 1;

          /* For each different sorting type... */
          switch (sid) {

            case 0: /* (  1 ,  1 ,  1 ) */
              t->ci = ci->progeny[7];
              t->cj = cj->progeny[0];
              t->flags = 0;
              break;

            case 1: /* (  1 ,  1 ,  0 ) */
              t->ci = ci->progeny[6];
              t->cj = cj->progeny[0];
              t->flags = 1;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 1, 0,
                                    ci->progeny[7], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[6], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              break;

            case 2: /* (  1 ,  1 , -1 ) */
              t->ci = ci->progeny[6];
              t->cj = cj->progeny[1];
              t->flags = 2;
              t->tight = 1;
              break;

            case 3: /* (  1 ,  0 ,  1 ) */
              t->ci = ci->progeny[5];
              t->cj = cj->progeny[0];
              t->flags = 3;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 3, 0,
                                    ci->progeny[7], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[5], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 6, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              break;

            case 4: /* (  1 ,  0 ,  0 ) */
              t->ci = ci->progeny[4];
              t->cj = cj->progeny[0];
              t->flags = 4;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 5, 0,
                                    ci->progeny[5], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[6], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 3, 0,
                                    ci->progeny[4], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 4, 0,
                                    ci->progeny[5], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 6, 0,
                                    ci->progeny[6], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[7], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 1, 0,
                                    ci->progeny[4], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[5], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 4, 0,
                                    ci->progeny[6], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 5, 0,
                                    ci->progeny[7], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[4], cj->progeny[3], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 1, 0,
                                    ci->progeny[5], cj->progeny[3], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 3, 0,
                                    ci->progeny[6], cj->progeny[3], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 4, 0,
                                    ci->progeny[7], cj->progeny[3], 1),
                  s);
              break;

            case 5: /* (  1 ,  0 , -1 ) */
              t->ci = ci->progeny[4];
              t->cj = cj->progeny[1];
              t->flags = 5;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 5, 0,
                                    ci->progeny[6], cj->progeny[3], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[4], cj->progeny[3], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[6], cj->progeny[1], 1),
                  s);
              break;

            case 6: /* (  1 , -1 ,  1 ) */
              t->ci = ci->progeny[5];
              t->cj = cj->progeny[2];
              t->flags = 6;
              t->tight = 1;
              break;

            case 7: /* (  1 , -1 ,  0 ) */
              t->ci = ci->progeny[4];
              t->cj = cj->progeny[3];
              t->flags = 6;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[5], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[4], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[5], cj->progeny[3], 1),
                  s);
              break;

            case 8: /* (  1 , -1 , -1 ) */
              t->ci = ci->progeny[4];
              t->cj = cj->progeny[3];
              t->flags = 8;
              t->tight = 1;
              break;

            case 9: /* (  0 ,  1 ,  1 ) */
              t->ci = ci->progeny[3];
              t->cj = cj->progeny[0];
              t->flags = 9;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 9, 0,
                                    ci->progeny[7], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[3], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              break;

            case 10: /* (  0 ,  1 ,  0 ) */
              t->ci = ci->progeny[2];
              t->cj = cj->progeny[0];
              t->flags = 10;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 11, 0,
                                    ci->progeny[3], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[6], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 6, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 9, 0,
                                    ci->progeny[2], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 10, 0,
                                    ci->progeny[3], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[6], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 7, 0,
                                    ci->progeny[7], cj->progeny[1], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 1, 0,
                                    ci->progeny[2], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[3], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 10, 0,
                                    ci->progeny[6], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 11, 0,
                                    ci->progeny[7], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[2], cj->progeny[5], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 1, 0,
                                    ci->progeny[3], cj->progeny[5], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 9, 0,
                                    ci->progeny[6], cj->progeny[5], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 10, 0,
                                    ci->progeny[7], cj->progeny[5], 1),
                  s);
              break;

            case 11: /* (  0 ,  1 , -1 ) */
              t->ci = ci->progeny[2];
              t->cj = cj->progeny[1];
              t->flags = 11;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 11, 0,
                                    ci->progeny[6], cj->progeny[5], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[2], cj->progeny[5], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 6, 0,
                                    ci->progeny[6], cj->progeny[1], 1),
                  s);
              break;

            case 12: /* (  0 ,  0 ,  1 ) */
              t->ci = ci->progeny[1];
              t->cj = cj->progeny[0];
              t->flags = 12;
              t->tight = 1;
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 11, 0,
                                    ci->progeny[3], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 5, 0,
                                    ci->progeny[5], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 2, 0,
                                    ci->progeny[7], cj->progeny[0], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 9, 0,
                                    ci->progeny[1], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 12, 0,
                                    ci->progeny[3], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 8, 0,
                                    ci->progeny[5], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 5, 0,
                                    ci->progeny[7], cj->progeny[2], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 3, 0,
                                    ci->progeny[1], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 6, 0,
                                    ci->progeny[3], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 12, 0,
                                    ci->progeny[5], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 11, 0,
                                    ci->progeny[7], cj->progeny[4], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                    ci->progeny[1], cj->progeny[6], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 3, 0,
                                    ci->progeny[3], cj->progeny[6], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 9, 0,
                                    ci->progeny[5], cj->progeny[6], 1),
                  s);
              scheduler_splittask(
                  scheduler_addtask(s, task_type_pair, t->subtype, 12, 0,
                                    ci->progeny[7], cj->progeny[6], 1),
                  s);
              break;
          } /* switch(sid) */
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        }

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        /* Otherwise, break it up if it is too large? */
      } else if (scheduler_doforcesplit && ci->split && cj->split &&
                 (ci->count > space_maxsize / cj->count)) {

        // message( "force splitting pair with %i and %i parts." , ci->count ,
        // cj->count );

        /* Replace the current task. */
        t->type = task_type_none;

        for (int j = 0; j < 8; j++)
          if (ci->progeny[j] != NULL)
            for (int k = 0; k < 8; k++)
              if (cj->progeny[k] != NULL) {
                struct task *tl =
                    scheduler_addtask(s, task_type_pair, t->subtype, 0, 0,
                                      ci->progeny[j], cj->progeny[k], 0);
                scheduler_splittask(tl, s);
                tl->flags = space_getsid(s->space, &t->ci, &t->cj, shift);
              }

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        /* Otherwise, if not spilt, stitch-up the sorting and drift. */
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      } else {

        /* Create the sort for ci. */
        lock_lock(&ci->lock);
        if (ci->sorts == NULL)
          ci->sorts = scheduler_addtask(s, task_type_sort, task_subtype_none,
                                        1 << sid, 0, ci, NULL, 0);
        else
          ci->sorts->flags |= (1 << sid);
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        scheduler_addunlock(s, ci->sorts, t);

        /* Create the drift for ci. */
        if (ci->drift == NULL) {
          ci->drift = scheduler_addtask(s, task_type_drift, task_subtype_none,
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          scheduler_addunlock(s, ci->drift, ci->sorts);
        }
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        lock_unlock_blind(&ci->lock);

        /* Create the sort for cj. */
        lock_lock(&cj->lock);
        if (cj->sorts == NULL)
          cj->sorts = scheduler_addtask(s, task_type_sort, task_subtype_none,
                                        1 << sid, 0, cj, NULL, 0);
        else
          cj->sorts->flags |= (1 << sid);
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        scheduler_addunlock(s, cj->sorts, t);
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        /* Create the drift for cj. */
        if (cj->drift == NULL) {
          cj->drift = scheduler_addtask(s, task_type_drift, task_subtype_none,
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                                        0, 0, cj, NULL, 0);
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          scheduler_addunlock(s, cj->drift, cj->sorts);
        }
        lock_unlock_blind(&cj->lock);
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      }

    } /* pair interaction? */

    /* Long-range gravity interaction ? */
    else if (t->type == task_type_grav_mm) {

      /* Get a handle on the cells involved. */
      struct cell *ci = t->ci;

      /* Safety thing */
      if (ci->gcount == 0) t->type = task_type_none;

    } /* gravity interaction? */
  }   /* iterate over the current task. */
}

/**
 * @brief Mapper function to split tasks that may be too large.
 *
 * @param map_data the tasks to process
 * @param num_elements the number of tasks.
 * @param extra_data The #scheduler we are working in.
 */
void scheduler_splittasks_mapper(void *map_data, int num_elements,
                                 void *extra_data) {

  /* Extract the parameters. */
  struct scheduler *s = (struct scheduler *)extra_data;
  struct task *tasks = (struct task *)map_data;
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  for (int ind = 0; ind < num_elements; ind++) {
    struct task *t = &tasks[ind];
    scheduler_splittask(t, s);
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  }
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}
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/**
 * @brief Splits all the tasks in the scheduler that are too large.
 *
 * @param s The #scheduler.
 */
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void scheduler_splittasks(struct scheduler *s) {
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  /* Call the mapper on each current task. */
  threadpool_map(s->threadpool, scheduler_splittasks_mapper, s->tasks,
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                 s->nr_tasks, sizeof(struct task), 1000, s);
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}

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/**
 * @brief Add a #task to the #scheduler.
 *
 * @param s The #scheduler we are working in.
 * @param type The type of the task.
 * @param subtype The sub-type of the task.
 * @param flags The flags of the task.
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 * @param wait The number of unsatisfied dependencies of this task.
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 * @param ci The first cell to interact.
 * @param cj The second cell to interact.
 * @param tight
 */
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struct task *scheduler_addtask(struct scheduler *s, enum task_types type,
                               enum task_subtypes subtype, int flags, int wait,
                               struct cell *ci, struct cell *cj, int tight) {
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  /* Get the next free task. */
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  const int ind = atomic_inc(&s->tasks_next);
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  /* Overflow? */
  if (ind >= s->size) error("Task list overflow.");

  /* Get a pointer to the new task. */
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  struct task *t = &s->tasks[ind];
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  /* Copy the data. */
  t->type = type;
  t->subtype = subtype;
  t->flags = flags;
  t->wait = wait;
  t->ci = ci;
  t->cj = cj;
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  t->skip = 1; /* Mark tasks as skip by default. */
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  t->tight = tight;
  t->implicit = 0;
  t->weight = 0;
  t->rank = 0;
  t->nr_unlock_tasks = 0;
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#ifdef SWIFT_DEBUG_TASKS
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  t->rid = -1;
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  t->tic = 0;
  t->toc = 0;
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#endif
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  /* Add an index for it. */
  // lock_lock( &s->lock );
  s->tasks_ind[atomic_inc(&s->nr_tasks)] = ind;
  // lock_unlock_blind( &s->lock );

  /* Return a pointer to the new task. */
  return t;
}
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/**
 * @brief Set the unlock pointers in each task.
 *
 * @param s The #scheduler.
 */
void scheduler_set_unlocks(struct scheduler *s) {

  /* Store the counts for each task. */
  int *counts;
  if ((counts = (int *)malloc(sizeof(int) * s->nr_tasks)) == NULL)
    error("Failed to allocate temporary counts array.");
  bzero(counts, sizeof(int) * s->nr_tasks);
  for (int k = 0; k < s->nr_unlocks; k++) counts[s->unlock_ind[k]] += 1;

  /* Compute the offset for each unlock block. */
  int *offsets;
  if ((offsets = (int *)malloc(sizeof(int) * (s->nr_tasks + 1))) == NULL)
    error("Failed to allocate temporary offsets array.");
  offsets[0] = 0;
  for (int k = 0; k < s->nr_tasks; k++) offsets[k + 1] = offsets[k] + counts[k];

  /* Create and fill a temporary array with the sorted unlocks. */
  struct task **unlocks;
  if ((unlocks = (struct task **)malloc(sizeof(struct task *) *
                                        s->size_unlocks)) == NULL)
    error("Failed to allocate temporary unlocks array.");
  for (int k = 0; k < s->nr_unlocks; k++) {
    const int ind = s->unlock_ind[k];
    unlocks[offsets[ind]] = s->unlocks[k];
    offsets[ind] += 1;
  }

  /* Swap the unlocks. */
  free(s->unlocks);
  s->unlocks = unlocks;

  /* Re-set the offsets. */
  offsets[0] = 0;
  for (int k = 1; k < s->nr_tasks; k++)
    offsets[k] = offsets[k - 1] + counts[k - 1];

  /* Set the unlocks in the tasks. */
  for (int k = 0; k < s->nr_tasks; k++) {
    struct task *t = &s->tasks[k];
    t->nr_unlock_tasks = counts[k];
    t->unlock_tasks = &s->unlocks[offsets[k]];
  }
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  /* Verify that there are no duplicate unlocks. */
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  for (int k = 0; k < s->nr_tasks; k++) {
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    struct task *t = &s->tasks[k];
    for (int i = 0; i < t->nr_unlock_tasks; i++) {
      for (int j = i + 1; j < t->nr_unlock_tasks; j++) {
        if (t->unlock_tasks[i] == t->unlock_tasks[j])
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          error("duplicate unlock! t->type=%s/%s unlocking type=%s/%s",
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                taskID_names[t->type], subtaskID_names[t->subtype],
                taskID_names[t->unlock_tasks[i]->type],
                subtaskID_names[t->unlock_tasks[i]->subtype]);
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      }
    }
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  }
#endif
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  /* Clean up. */
  free(counts);
  free(offsets);
}

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/**
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 * @brief Sort the tasks in topological order over all queues.
 *
 * @param s The #scheduler.
 */
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void scheduler_ranktasks(struct scheduler *s) {

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  struct task *tasks = s->tasks;
  int *tid = s->tasks_ind;
  const int nr_tasks = s->nr_tasks;
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  /* Run through the tasks and get all the waits right. */
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  for (int i = 0; i < nr_tasks; i++) {
    struct task *t = &tasks[i];

    // Increment the waits of the dependances
    for (int k = 0; k < t->nr_unlock_tasks; k++) {
      t->unlock_tasks[k]->wait++;
    }
  }
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  /* Load the tids of tasks with no waits. */
  int left = 0;
  for (int k = 0; k < nr_tasks; k++)
    if (tasks[k].wait == 0) {
      tid[left] = k;
      left += 1;
    }

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  /* Main loop. */
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  for (int j = 0, rank = 0; left < nr_tasks; rank++) {
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    /* Did we get anything? */
    if (j == left) error("Unsatisfiable task dependencies detected.");
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    const int left_old = left;
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    /* Unlock the next layer of tasks. */
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    for (; j < left_old; j++) {
      struct task *t = &tasks[tid[j]];
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      t->rank = rank;
      /* message( "task %i of type %s has rank %i." , i ,
          (t->type == task_type_self) ? "self" : (t->type == task_type_pair) ?
         "pair" : "sort" , rank ); */
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      for (int k = 0; k < t->nr_unlock_tasks; k++) {
        struct task *u = t->unlock_tasks[k];
        if (--u->wait == 0) {
          tid[left] = u - tasks;
          left += 1;
        }
      }
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    }

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    /* Move back to the old left (like Sanders). */
    j = left_old;
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  }

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#ifdef SWIFT_DEBUG_CHECKS
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  /* Verify that the tasks were ranked correctly. */
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  for (int k = 1; k < s->nr_tasks; k++)
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    if (tasks[tid[k - 1]].rank > tasks[tid[k - 1]].rank)
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      error("Task ranking failed.");
#endif
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}
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/**
 * @brief (Re)allocate the task arrays.
 *
 * @param s The #scheduler.
 * @param size The maximum number of tasks in the #scheduler.
 */
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void scheduler_reset(struct scheduler *s, int size) {
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  /* Do we need to re-allocate? */
  if (size > s->size) {
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    /* Free existing task lists if necessary. */
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    if (s->tasks != NULL) free(s->tasks);
    if (s->tasks_ind != NULL) free(s->tasks_ind);
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    if (s->tid_active != NULL) free(s->tid_active);
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    /* Allocate the new lists. */
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    if (posix_memalign((void *)&s->tasks, task_align,
                       size * sizeof(struct task)) != 0)
      error("Failed to allocate task array.");

    if ((s->tasks_ind = (int *)malloc(sizeof(int) * size)) == NULL)
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      error("Failed to allocate task lists.");
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    if ((s->tid_active = (int *)malloc(sizeof(int) * size)) == NULL)
      error("Failed to allocate aactive task lists.");
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  }
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  /* Reset the counters. */
  s->size = size;
  s->nr_tasks = 0;
  s->tasks_next = 0;
  s->waiting = 0;
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  s->nr_unlocks = 0;
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  s->completed_unlock_writes = 0;
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  s->active_count = 0;
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  /* Set the task pointers in the queues. */
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  for (int k = 0; k < s->nr_queues; k++) s->queues[k].tasks = s->tasks;
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}
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/**
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 * @brief Compute the task weights
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 *
 * @param s The #scheduler.
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 * @param verbose Are we talkative?
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 */
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void scheduler_reweight(struct scheduler *s, int verbose) {
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  const int nr_tasks = s->nr_tasks;
  int *tid = s->tasks_ind;
  struct task *tasks = s->tasks;
  const int nodeID = s->nodeID;
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  const float sid_scale[13] = {0.1897, 0.4025, 0.1897, 0.4025, 0.5788,
                               0.4025, 0.1897, 0.4025, 0.1897, 0.4025,
                               0.5788, 0.4025, 0.5788};
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  const float wscale = 0.001;
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  const ticks tic = getticks();
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  /* Run through the tasks backwards and set their weights. */
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  for (int k = nr_tasks - 1; k >= 0; k--) {
    struct task *t = &tasks[tid[k]];
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    t->weight = 0;
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    for (int j = 0; j < t->nr_unlock_tasks; j++)
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      if (t->unlock_tasks[j]->weight > t->weight)
        t->weight = t->unlock_tasks[j]->weight;
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    int cost = 0;
    switch (t->type) {
      case task_type_sort:
        cost = wscale * intrinsics_popcount(t->flags) * t->ci->count *
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               (sizeof(int) * 8 - intrinsics_clz(t->ci->count));
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        break;
      case task_type_self:
        cost = 1 * wscale * t->ci->count * t->ci->count;
        break;
      case task_type_pair:
        if (t->ci->nodeID != nodeID || t->cj->nodeID != nodeID)
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          cost = 3 * wscale * t->ci->count * t->cj->count * sid_scale[t->flags];
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        else
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          cost = 2 * wscale * t->ci->count * t->cj->count * sid_scale[t->flags];
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        break;
      case task_type_sub_pair:
        if (t->ci->nodeID != nodeID || t->cj->nodeID != nodeID) {
          if (t->flags < 0)
            cost = 3 * wscale * t->ci->count * t->cj->count;
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          else
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            cost =
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                3 * wscale * t->ci->count * t->cj->count * sid_scale[t->flags];
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        } else {
          if (t->flags < 0)
            cost = 2 * wscale * t->ci->count * t->cj->count;
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          else
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            cost =
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                2 * wscale * t->ci->count * t->cj->count * sid_scale[t->flags];
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        }
        break;
      case task_type_sub_self:
        cost = 1 * wscale * t->ci->count * t->ci->count;
        break;
      case task_type_ghost:
        if (t->ci == t->ci->super) cost = wscale * t->ci->count;
        break;
      case task_type_kick:
        cost = wscale * t->ci->count;
        break;
      case task_type_init:
        cost = wscale * t->ci->count;
        break;
      default:
        cost = 0;
        break;
    }
#if defined(WITH_MPI) && defined(HAVE_METIS)
    t->cost = cost;
#endif
    t->weight += cost;
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  }
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  if (verbose)
    message("took %.3f %s.", clocks_from_ticks(getticks() - tic),
            clocks_getunit());