starpu-max/src/sched_policies/heft.c

/* StarPU --- Runtime system for heterogeneous multicore architectures.
 *
 * Copyright (C) 2010, 2011-2012  Université de Bordeaux 1
 * Copyright (C) 2010, 2011, 2012  Centre National de la Recherche Scientifique
 * Copyright (C) 2011  Télécom-SudParis
 * Copyright (C) 2011  INRIA
 *
 * 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.
 *
 * 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.
 */

/* Distributed queues using performance modeling to assign tasks */

#include <float.h>

#include <core/workers.h>
#include <core/perfmodel/perfmodel.h>
#include <core/task_bundle.h>
#include <core/workers.h>
#include <starpu_parameters.h>
#include <starpu_task_bundle.h>
#include <starpu_top.h>

#ifndef DBL_MIN
#define DBL_MIN __DBL_MIN__
#endif

#ifndef DBL_MAX
#define DBL_MAX __DBL_MAX__
#endif

static double exp_start[STARPU_NMAXWORKERS]; /* of the first queued task */
static double exp_end[STARPU_NMAXWORKERS];   /* of the set of queued tasks */
static double exp_len[STARPU_NMAXWORKERS];   /* of the last queued task */
static double ntasks[STARPU_NMAXWORKERS];

typedef struct {
	double alpha;
	double beta;
	double _gamma;
	double idle_power;
} heft_data;

const float alpha_minimum=0;
const float alpha_maximum=10.0;
const float beta_minimum=0;
const float beta_maximum=10.0;
const float gamma_minimum=0;
const float gamma_maximum=10000.0;
const float idle_power_minimum=0;
const float idle_power_maximum=10000.0;

static void param_modified(struct starpu_top_param* d)
{
	//just to show parameter modification
	fprintf(stderr,"%s has been modified : %f !\n", d->name, d->value);
}


static void heft_add_workers(unsigned sched_ctx_id, int *workerids, unsigned nworkers)
{
	int workerid;
	unsigned i;
	for (i = 0; i < nworkers; i++)
	{
		workerid = workerids[i];
		struct _starpu_worker *workerarg = _starpu_get_worker_struct(workerid);
		/* init these structures only once for each worker */
		if(!workerarg->has_prev_init)
		{
			exp_start[workerid] = starpu_timing_now();
			exp_len[workerid] = 0.0;
			exp_end[workerid] = exp_start[workerid]; 
			ntasks[workerid] = 0;
			workerarg->has_prev_init = 1;
		}
		
		/* we push the tasks on the local lists of the workers
		   therefore the synchronisations mechanisms of the strategy
		   are the global ones */
		starpu_worker_set_sched_condition(sched_ctx_id, workerid, &workerarg->sched_mutex, &workerarg->sched_cond);
	}
}

static void heft_remove_workers(unsigned sched_ctx_id, int *workerids, unsigned nworkers)
{
	int workerid;
	unsigned i;
	for (i = 0; i < nworkers; i++)
	{
		workerid = workerids[i];
		starpu_worker_set_sched_condition(sched_ctx_id, workerid, NULL, NULL);
	}
}

static void heft_init(unsigned sched_ctx_id)
{
	starpu_create_worker_collection_for_sched_ctx(sched_ctx_id, WORKER_LIST);

	heft_data *hd = (heft_data*)malloc(sizeof(heft_data));
	hd->alpha = _STARPU_DEFAULT_ALPHA;
	hd->beta = _STARPU_DEFAULT_BETA;
	hd->_gamma = _STARPU_DEFAULT_GAMMA;
	hd->idle_power = 0.0;
	
	starpu_set_sched_ctx_policy_data(sched_ctx_id, (void*)hd);

	const char *strval_alpha = getenv("STARPU_SCHED_ALPHA");
	if (strval_alpha)
		hd->alpha = atof(strval_alpha);

	const char *strval_beta = getenv("STARPU_SCHED_BETA");
	if (strval_beta)
		hd->beta = atof(strval_beta);

	const char *strval_gamma = getenv("STARPU_SCHED_GAMMA");
	if (strval_gamma)
		hd->_gamma = atof(strval_gamma);

	const char *strval_idle_power = getenv("STARPU_IDLE_POWER");
	if (strval_idle_power)
		hd->idle_power = atof(strval_idle_power);

	starpu_top_register_parameter_float("HEFT_ALPHA", &hd->alpha, alpha_minimum,alpha_maximum,param_modified);
	starpu_top_register_parameter_float("HEFT_BETA", &hd->beta, beta_minimum,beta_maximum,param_modified);
	starpu_top_register_parameter_float("HEFT_GAMMA", &hd->_gamma, gamma_minimum,gamma_maximum,param_modified);
	starpu_top_register_parameter_float("HEFT_IDLE_POWER", &hd->idle_power, idle_power_minimum,idle_power_maximum,param_modified);
}


/* heft_pre_exec_hook is called right after the data transfer is done and right before
 * the computation to begin, it is useful to update more precisely the value
 * of the expected start, end, length, etc... */
static void heft_pre_exec_hook(struct starpu_task *task)
{
	unsigned sched_ctx_id = task->sched_ctx;
	int workerid = starpu_worker_get_id();
	double model = task->predicted;
	double transfer_model = task->predicted_transfer;

	pthread_mutex_t *sched_mutex;
	pthread_cond_t *sched_cond;
	starpu_worker_get_sched_condition(sched_ctx_id, workerid, &sched_mutex, &sched_cond);

	/* Once the task is executing, we can update the predicted amount
	 * of work. */
	_STARPU_PTHREAD_MUTEX_LOCK(sched_mutex);
	exp_len[workerid] -= model + transfer_model;
	exp_start[workerid] = starpu_timing_now() + model;
	exp_end[workerid] = exp_start[workerid] + exp_len[workerid];
	ntasks[workerid]--;
	_STARPU_PTHREAD_MUTEX_UNLOCK(sched_mutex);
}

static void heft_push_task_notify(struct starpu_task *task, int workerid)
{
	unsigned sched_ctx_id = task->sched_ctx;
	/* Compute the expected penality */
	enum starpu_perf_archtype perf_arch = starpu_worker_get_perf_archtype(workerid);
	unsigned memory_node = starpu_worker_get_memory_node(workerid);

	double predicted = starpu_task_expected_length(task, perf_arch,
			_starpu_get_job_associated_to_task(task)->nimpl);

	double predicted_transfer = starpu_task_expected_data_transfer_time(memory_node, task);
	pthread_mutex_t *sched_mutex;
	pthread_cond_t *sched_cond;
	starpu_worker_get_sched_condition(sched_ctx_id, workerid, &sched_mutex, &sched_cond);


	/* Update the predictions */
	_STARPU_PTHREAD_MUTEX_LOCK(sched_mutex);
	/* Sometimes workers didn't take the tasks as early as we expected */
	exp_start[workerid] = STARPU_MAX(exp_start[workerid], starpu_timing_now());
	exp_end[workerid] = exp_start[workerid] + exp_len[workerid];

	/* If there is no prediction available, we consider the task has a null length */
	if (!isnan(predicted))
	{
		task->predicted = predicted;
		exp_end[workerid] += predicted;
		exp_len[workerid] += predicted;
	}

	/* If there is no prediction available, we consider the task has a null length */
	if (!isnan(predicted_transfer))
	{
		if (starpu_timing_now() + predicted_transfer < exp_end[workerid])
		{
			/* We may hope that the transfer will be finished by
			 * the start of the task. */
			predicted_transfer = 0;
		}
		else
		{
			/* The transfer will not be finished by then, take the
			 * remainder into account */
			predicted_transfer = (starpu_timing_now() + predicted_transfer) - exp_end[workerid];
		}
		task->predicted_transfer = predicted_transfer;
		exp_end[workerid] += predicted_transfer;
		exp_len[workerid] += predicted_transfer;
	}

	ntasks[workerid]++;

	_STARPU_PTHREAD_MUTEX_UNLOCK(sched_mutex);
}

static int push_task_on_best_worker(struct starpu_task *task, int best_workerid, double predicted, double predicted_transfer, int prio, unsigned sched_ctx_id)
 {
	/* make sure someone coule execute that task ! */
	STARPU_ASSERT(best_workerid != -1);

	pthread_mutex_t *sched_mutex;
	pthread_cond_t *sched_cond;
	starpu_worker_get_sched_condition(sched_ctx_id, best_workerid, &sched_mutex, &sched_cond);

#ifdef STARPU_USE_SCHED_CTX_HYPERVISOR
	starpu_call_pushed_task_cb(best_workerid, sched_ctx_id);
#endif //STARPU_USE_SCHED_CTX_HYPERVISOR

	_STARPU_PTHREAD_MUTEX_LOCK(sched_mutex);

	/* Sometimes workers didn't take the tasks as early as we expected */
	exp_start[best_workerid] = STARPU_MAX(exp_start[best_workerid], starpu_timing_now());
	exp_end[best_workerid] = exp_start[best_workerid] + exp_len[best_workerid];

	exp_end[best_workerid] += predicted;
	exp_len[best_workerid] += predicted;

	if (starpu_timing_now() + predicted_transfer < exp_end[best_workerid])
	{
		/* We may hope that the transfer will be finished by
		 * the start of the task. */
		predicted_transfer = 0;
	}
	else
	{
		/* The transfer will not be finished by then, take the
		 * remainder into account */
		predicted_transfer = (starpu_timing_now() + predicted_transfer) - exp_end[best_workerid];
	}
	exp_end[best_workerid] += predicted_transfer;
	exp_len[best_workerid] += predicted_transfer;

	ntasks[best_workerid]++;
	_STARPU_PTHREAD_MUTEX_UNLOCK(sched_mutex);

	task->predicted = predicted;
	task->predicted_transfer = predicted_transfer;

	if (_starpu_top_status_get())
		_starpu_top_task_prevision(task, best_workerid,
					(unsigned long long)(exp_end[best_workerid]-predicted)/1000,
					(unsigned long long)exp_end[best_workerid]/1000);

	if (starpu_get_prefetch_flag())
	{
		unsigned memory_node = starpu_worker_get_memory_node(best_workerid);
		starpu_prefetch_task_input_on_node(task, memory_node);
	}


	//_STARPU_DEBUG("Heft : pushing local task\n");
	return starpu_push_local_task(best_workerid, task, prio);
}

/* TODO: factorize with dmda!! */
static void compute_all_performance_predictions(struct starpu_task *task,
						double (*local_task_length)[STARPU_MAXIMPLEMENTATIONS], 
						double (*exp_end)[STARPU_MAXIMPLEMENTATIONS],
						double *max_exp_endp, double *best_exp_endp,
						double (*local_data_penalty)[STARPU_MAXIMPLEMENTATIONS],
						double (*local_power)[STARPU_MAXIMPLEMENTATIONS], 
						int *forced_worker, int *forced_impl,
						starpu_task_bundle_t bundle,
						unsigned sched_ctx_id)
{
	int calibrating = 0;
	double max_exp_end = DBL_MIN;
	double best_exp_end = DBL_MAX;
	int ntasks_best = -1;
	int nimpl_best = 0;
	double ntasks_best_end = 0.0;

	/* A priori, we know all estimations */
	int unknown = 0;
	int worker, worker_ctx = 0;
	unsigned nimpl;

	struct worker_collection *workers = starpu_get_worker_collection_of_sched_ctx(sched_ctx_id);

	while(workers->has_next(workers))
	{
		worker = workers->get_next(workers);
		for (nimpl = 0; nimpl <STARPU_MAXIMPLEMENTATIONS; nimpl++) 
		{
			/* Sometimes workers didn't take the tasks as early as we expected */
			pthread_mutex_t *sched_mutex;
			pthread_cond_t *sched_cond;
			starpu_worker_get_sched_condition(sched_ctx_id, worker, &sched_mutex, &sched_cond);
			_STARPU_PTHREAD_MUTEX_LOCK(sched_mutex);
			exp_start[worker] = STARPU_MAX(exp_start[worker], starpu_timing_now());
			exp_end[worker_ctx][nimpl] = exp_start[worker] + exp_len[worker];
			if (exp_end[worker_ctx][nimpl] > max_exp_end)
 				max_exp_end = exp_end[worker_ctx][nimpl];
			_STARPU_PTHREAD_MUTEX_UNLOCK(sched_mutex);
			if (!starpu_worker_can_execute_task(worker, task, nimpl))
			{
				/* no one on that queue may execute this task */
//				worker_ctx++;
				continue;
			}

			enum starpu_perf_archtype perf_arch = starpu_worker_get_perf_archtype(worker);
			unsigned memory_node = starpu_worker_get_memory_node(worker);

			if (bundle)
			{
				/* TODO : conversion time */
				local_task_length[worker_ctx][nimpl] = starpu_task_bundle_expected_length(bundle, perf_arch, nimpl);
				local_data_penalty[worker_ctx][nimpl] = starpu_task_bundle_expected_data_transfer_time(bundle, memory_node);
				local_power[worker_ctx][nimpl] = starpu_task_bundle_expected_power(bundle, perf_arch, nimpl);
				//_STARPU_DEBUG("Scheduler heft bundle: task length (%lf) local power (%lf) worker (%u) kernel (%u) \n", local_task_length[worker_ctx],local_power[worker_ctx],worker,nimpl);
			}
			else 
			{
				local_task_length[worker_ctx][nimpl] = starpu_task_expected_length(task, perf_arch, nimpl);
				local_data_penalty[worker_ctx][nimpl] = starpu_task_expected_data_transfer_time(memory_node, task);
				local_power[worker_ctx][nimpl] = starpu_task_expected_power(task, perf_arch, nimpl);
				double conversion_time = starpu_task_expected_conversion_time(task, perf_arch, nimpl);
				if (conversion_time > 0.0)
					local_task_length[worker_ctx][nimpl] += conversion_time;
				//_STARPU_DEBUG("Scheduler heft bundle: task length (%lf) local power (%lf) worker (%u) kernel (%u) \n", local_task_length[worker_ctx],local_power[worker_ctx],worker,nimpl);
			}

			double ntasks_end = ntasks[worker] / starpu_worker_get_relative_speedup(perf_arch);

			if (ntasks_best == -1
			    || (!calibrating && ntasks_end < ntasks_best_end) /* Not calibrating, take better worker */
			    || (!calibrating && isnan(local_task_length[worker_ctx][nimpl])) /* Not calibrating but this worker is being calibrated */
			    || (calibrating && isnan(local_task_length[worker_ctx][nimpl]) && ntasks_end < ntasks_best_end) /* Calibrating, compete this worker with other non-calibrated */
				)
			{
				ntasks_best_end = ntasks_end;
				ntasks_best = worker;
				nimpl_best = nimpl;
			}

			if (isnan(local_task_length[worker_ctx][nimpl]))
				/* we are calibrating, we want to speed-up calibration time
				 * so we privilege non-calibrated tasks (but still
				 * greedily distribute them to avoid dumb schedules) */
				calibrating = 1;

			if (isnan(local_task_length[worker_ctx][nimpl])
				|| _STARPU_IS_ZERO(local_task_length[worker_ctx][nimpl]))
				/* there is no prediction available for that task
				 * with that arch (yet or at all), so switch to a greedy strategy */
				unknown = 1;

			if (unknown)
				continue;

			exp_end[worker_ctx][nimpl] = exp_start[worker] + exp_len[worker] + local_task_length[worker_ctx][nimpl];
			
			if (exp_end[worker_ctx][nimpl] < best_exp_end)
			{
				/* a better solution was found */
				best_exp_end = exp_end[worker_ctx][nimpl];
				nimpl_best = nimpl;
			}

			if (isnan(local_power[worker_ctx][nimpl]))
				local_power[worker_ctx][nimpl] = 0.;

		}
		worker_ctx++;
	}

	*forced_worker = unknown?ntasks_best:-1;
	*forced_impl = unknown?nimpl_best:-1;

	*best_exp_endp = best_exp_end;
	*max_exp_endp = max_exp_end;
}

static int push_conversion_tasks(struct starpu_task *task, unsigned int workerid)
{
	unsigned i;
	int ret;
	unsigned int node = starpu_worker_get_memory_node(workerid);
	unsigned sched_ctx_id = task->sched_ctx;
	pthread_mutex_t *sched_mutex;
        pthread_cond_t *sched_cond;
        starpu_worker_get_sched_condition(sched_ctx_id, workerid, &sched_mutex, &sched_cond);

	_STARPU_PTHREAD_MUTEX_LOCK(&sched_mutex[workerid]);
	for (i = 0; i < task->cl->nbuffers; i++)
	{
		struct starpu_task *conversion_task;
		starpu_data_handle_t handle;

		handle = task->handles[i];
		if (!_starpu_handle_needs_conversion_task(handle, node))
			continue;

		conversion_task = _starpu_create_conversion_task(handle, node);
		conversion_task->execute_on_a_specific_worker = 1;
		conversion_task->workerid = workerid;
		conversion_task->mf_skip = 1;
		handle->mf_node = node;
		ret = _starpu_task_submit_conversion_task(conversion_task, workerid);
		STARPU_ASSERT(ret == 0);
	}

	task->execute_on_a_specific_worker = 1;
	task->workerid = workerid;
	task->mf_skip= 1;
	_STARPU_PTHREAD_MUTEX_UNLOCK(&sched_mutex[workerid]);

	return 0;
}

/* TODO: factorize with dmda */
static int _heft_push_task(struct starpu_task *task, unsigned prio, unsigned sched_ctx_id)
{
	heft_data *hd = (heft_data*)starpu_get_sched_ctx_policy_data(sched_ctx_id);
	int worker, worker_ctx = 0;
	unsigned nimpl;
	int best = -1, best_in_ctx = -1;
	int selected_impl= -1;

	/* this flag is set if the corresponding worker is selected because
	   there is no performance prediction available yet */
	int forced_worker;
	int forced_impl;
	struct worker_collection *workers = starpu_get_worker_collection_of_sched_ctx(sched_ctx_id);

	unsigned nworkers_ctx = workers->nworkers;
	double local_task_length[nworkers_ctx][STARPU_MAXIMPLEMENTATIONS];
	double local_data_penalty[nworkers_ctx][STARPU_MAXIMPLEMENTATIONS];
	double local_power[nworkers_ctx][STARPU_MAXIMPLEMENTATIONS];
	double exp_end[nworkers_ctx][STARPU_MAXIMPLEMENTATIONS];
	double max_exp_end = 0.0;

	double best_exp_end;

	/*
	 *	Compute the expected end of the task on the various workers,
	 *	and detect if there is some calibration that needs to be done.
	 */

	starpu_task_bundle_t bundle = NULL; //task->bundle;

	if(workers->init_cursor)
		workers->init_cursor(workers);

	compute_all_performance_predictions(task, local_task_length, exp_end,
					&max_exp_end, &best_exp_end,
					local_data_penalty,
					local_power, &forced_worker, &forced_impl,
					bundle, sched_ctx_id);

	/* If there is no prediction available for that task with that arch we
	 * want to speed-up calibration time so we force this measurement */
	if (forced_worker != -1)
	{
		_starpu_get_job_associated_to_task(task)->nimpl = forced_impl;

		if (_starpu_task_uses_multiformat_handles(task) && !task->mf_skip)
		{
			/*
			 * Our task uses multiformat handles, which may need to be converted.
			 */
			push_conversion_tasks(task, forced_worker);
			prio = 0;
		}
		return push_task_on_best_worker(task, forced_worker, 0.0, 0.0, prio, sched_ctx_id);
	}

	/*
	 *	Determine which worker optimizes the fitness metric which is a
	 *	trade-off between load-balacing, data locality, and energy
	 *	consumption.
	 */
	
	double fitness[nworkers_ctx][STARPU_MAXIMPLEMENTATIONS];
	double best_fitness = -1;

	while(workers->has_next(workers))
	{
		worker = workers->get_next(workers);
		for (nimpl = 0; nimpl < STARPU_MAXIMPLEMENTATIONS; nimpl++)
		{
			if (!starpu_worker_can_execute_task(worker, task, nimpl))
			{
				/* no one on that queue may execute this task */
				//worker_ctx++;
				continue;
			}


			fitness[worker_ctx][nimpl] = hd->alpha*(exp_end[worker_ctx][nimpl] - best_exp_end) 
						+ hd->beta*(local_data_penalty[worker_ctx][nimpl])
						+ hd->_gamma*(local_power[worker_ctx][nimpl]);

			if (exp_end[worker_ctx][nimpl] > max_exp_end)
				/* This placement will make the computation
				 * longer, take into account the idle
				 * consumption of other cpus */
				fitness[worker_ctx][nimpl] += hd->_gamma * hd->idle_power * (exp_end[worker_ctx][nimpl] - max_exp_end) / 1000000.0;
			
			if (best == -1 || fitness[worker_ctx][nimpl] < best_fitness)
			{
				/* we found a better solution */
				best_fitness = fitness[worker_ctx][nimpl];
				best = worker;
				best_in_ctx = worker_ctx;
				selected_impl = nimpl;
			}
		}
		worker_ctx++;
	}

	/* By now, we must have found a solution */
	STARPU_ASSERT(best != -1);

	/* we should now have the best worker in variable "best" */
	double model_best, transfer_model_best;

	if (bundle)
	{
		/* If we have a task bundle, we have computed the expected
		 * length for the entire bundle, but not for the task alone. */
		enum starpu_perf_archtype perf_arch = starpu_worker_get_perf_archtype(best);
		unsigned memory_node = starpu_worker_get_memory_node(best);
		model_best = starpu_task_expected_length(task, perf_arch, selected_impl);
		transfer_model_best = starpu_task_expected_data_transfer_time(memory_node, task);

		/* Remove the task from the bundle since we have made a
		 * decision for it, and that other tasks should not consider it
		 * anymore. */
		starpu_task_bundle_remove(bundle, task);
	}
	else 
	{
		model_best = local_task_length[best_in_ctx][selected_impl];
		transfer_model_best = local_data_penalty[best_in_ctx][selected_impl];
	}

	if(workers->init_cursor)
		workers->deinit_cursor(workers);

	_starpu_get_job_associated_to_task(task)->nimpl = selected_impl;

	if (_starpu_task_uses_multiformat_handles(task) && !task->mf_skip)
	{
		/*
		 * Our task uses multiformat handles, which may need to be converted.
		 */
		push_conversion_tasks(task, forced_worker);
		prio = 0;
	}

	return push_task_on_best_worker(task, best, model_best, transfer_model_best, prio, sched_ctx_id);
}

static int heft_push_task(struct starpu_task *task)
{
	unsigned sched_ctx_id = task->sched_ctx;
	pthread_mutex_t *changing_ctx_mutex = starpu_get_changing_ctx_mutex(sched_ctx_id);
	unsigned nworkers; 
	int ret_val = -1;
	if (task->priority > 0)
	{
		_STARPU_PTHREAD_MUTEX_LOCK(changing_ctx_mutex);
		nworkers = starpu_get_nworkers_of_sched_ctx(sched_ctx_id);
		if(nworkers == 0)
		{
			_STARPU_PTHREAD_MUTEX_UNLOCK(changing_ctx_mutex);
			return ret_val;
		}

		ret_val = _heft_push_task(task, 1, sched_ctx_id);
		_STARPU_PTHREAD_MUTEX_UNLOCK(changing_ctx_mutex);
		return ret_val;
	}

	_STARPU_PTHREAD_MUTEX_LOCK(changing_ctx_mutex);
	nworkers = starpu_get_nworkers_of_sched_ctx(sched_ctx_id);
	if(nworkers == 0)
	{
		_STARPU_PTHREAD_MUTEX_UNLOCK(changing_ctx_mutex);
		return ret_val;
	}

	ret_val = _heft_push_task(task, 0, sched_ctx_id);
	_STARPU_PTHREAD_MUTEX_UNLOCK(changing_ctx_mutex);
	return ret_val;
}

static void heft_deinit(unsigned sched_ctx_id) 
{
	heft_data *ht = (heft_data*)starpu_get_sched_ctx_policy_data(sched_ctx_id);
	free(ht);
	starpu_delete_worker_collection_for_sched_ctx(sched_ctx_id);
}

struct starpu_sched_policy heft_policy = 
{
	.init_sched = heft_init,
	.deinit_sched = heft_deinit,
	.push_task = heft_push_task,
	.push_task_notify = heft_push_task_notify,
	.pop_task = NULL,
	.pop_every_task = NULL,
	.pre_exec_hook = heft_pre_exec_hook,
	.post_exec_hook = NULL,
	.add_workers = heft_add_workers	,
	.remove_workers = heft_remove_workers,
	.policy_name = "heft",
	.policy_description = "Heterogeneous Earliest Finish Task"
};