StarPU Handbook

Data Structures | Macros | Typedefs | Functions
Scheduling Policy

TODO. While StarPU comes with a variety of scheduling policies (see Task Scheduling Policies), it may sometimes be desirable to implement custom policies to address specific problems. The API described below allows users to write their own scheduling policy. More...

## Data Structures
struct | starpu_sched_policy

## Macros
#define | STARPU_NMAX_SCHED_CTXS
#define | STARPU_MAXIMPLEMENTATIONS

## Typedefs
typedef void(* | starpu_notify_ready_soon_func) (void *data, struct starpu_task *task, double delay)

## Functions
struct starpu_sched_policy ** | starpu_sched_get_predefined_policies ()
void | starpu_worker_get_sched_condition (int workerid, starpu_pthread_mutex_t **sched_mutex, starpu_pthread_cond_t **sched_cond)
unsigned long | starpu_task_get_job_id (struct starpu_task *task)
int | starpu_sched_get_min_priority (void)
int | starpu_sched_get_max_priority (void)
int | starpu_sched_set_min_priority (int min_prio)
int | starpu_sched_set_max_priority (int max_prio)
int | starpu_worker_can_execute_task (unsigned workerid, struct starpu_task *task, unsigned nimpl)
int | starpu_worker_can_execute_task_impl (unsigned workerid, struct starpu_task *task, unsigned *impl_mask)
int | starpu_worker_can_execute_task_first_impl (unsigned workerid, struct starpu_task *task, unsigned *nimpl)
int | starpu_push_local_task (int workerid, struct starpu_task *task, int back)
int | starpu_push_task_end (struct starpu_task *task)
int | starpu_get_prefetch_flag (void)
int | starpu_prefetch_task_input_on_node_prio (struct starpu_task *task, unsigned node, int prio)
int | starpu_prefetch_task_input_on_node (struct starpu_task *task, unsigned node)
int | starpu_idle_prefetch_task_input_on_node_prio (struct starpu_task *task, unsigned node, int prio)
int | starpu_idle_prefetch_task_input_on_node (struct starpu_task *task, unsigned node)
int | starpu_prefetch_task_input_for_prio (struct starpu_task *task, unsigned worker, int prio)
int | starpu_prefetch_task_input_for (struct starpu_task *task, unsigned worker)
int | starpu_idle_prefetch_task_input_for_prio (struct starpu_task *task, unsigned worker, int prio)
int | starpu_idle_prefetch_task_input_for (struct starpu_task *task, unsigned worker)
uint32_t | starpu_task_footprint (struct starpu_perfmodel *model, struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
uint32_t | starpu_task_data_footprint (struct starpu_task *task)
double | starpu_task_expected_length (struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
double | starpu_worker_get_relative_speedup (struct starpu_perfmodel_arch *perf_arch)
double | starpu_task_expected_data_transfer_time (unsigned memory_node, struct starpu_task *task)
double | starpu_task_expected_data_transfer_time_for (struct starpu_task *task, unsigned worker)
double | starpu_data_expected_transfer_time (starpu_data_handle_t handle, unsigned memory_node, enum starpu_data_access_mode mode)
double | starpu_task_expected_energy (struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
double | starpu_task_expected_conversion_time (struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
void | starpu_task_notify_ready_soon_register (starpu_notify_ready_soon_func f, void *data)
void | starpu_sched_ctx_worker_shares_tasks_lists (int workerid, int sched_ctx_id)
void | starpu_sched_task_break (struct starpu_task *task)

## Worker operations
int | starpu_wake_worker_relax (int workerid)
int | starpu_wake_worker_no_relax (int workerid)
int | starpu_wake_worker_locked (int workerid)
int | starpu_wake_worker_relax_light (int workerid)

## Detailed Description

TODO. While StarPU comes with a variety of scheduling policies (see Task Scheduling Policies), it may sometimes be desirable to implement custom policies to address specific problems. The API described below allows users to write their own scheduling policy.

## Data Structure Documentation

## ◆ starpu_sched_policy

struct starpu_sched_policy

Contain all the methods that implement a scheduling policy. An application may specify which scheduling strategy in the field starpu_conf::sched_policy passed to the function starpu_init().

For each task going through the scheduler, the following methods get called in the given order:

- starpu_sched_policy::submit_hook when the task is submitted
- starpu_sched_policy::push_task when the task becomes ready. The scheduler is here given the task
- starpu_sched_policy::pop_task when the worker is idle. The scheduler here gives back the task to the core. It must not access this task any more
- starpu_sched_policy::pre_exec_hook right before the worker actually starts the task computation (after transferring any missing data).
- starpu_sched_policy::post_exec_hook right after the worker actually completes the task computation.

For each task not going through the scheduler (because starpu_task::execute_on_a_specific_worker was set), these get called:

- starpu_sched_policy::submit_hook when the task is submitted
- starpu_sched_policy::push_task_notify when the task becomes ready. This is just a notification, the scheduler does not have to do anything about the task.
- starpu_sched_policy::pre_exec_hook right before the worker actually starts the task computation (after transferring any missing data).
- starpu_sched_policy::post_exec_hook right after the worker actually completes the task computation.

### Data Fields
void(* | init_sched )(unsigned sched_ctx_id)
void(* | deinit_sched )(unsigned sched_ctx_id)
int(* | push_task )(struct starpu_task *)
double(* | simulate_push_task )(struct starpu_task *)
void(* | push_task_notify )(struct starpu_task *, int workerid, int perf_workerid, unsigned sched_ctx_id)
struct starpu_task *(* | pop_task )(unsigned sched_ctx_id)
struct starpu_task *(* | pop_every_task )(unsigned sched_ctx_id)
void(* | submit_hook )(struct starpu_task *task)
void(* | pre_exec_hook )(struct starpu_task *, unsigned sched_ctx_id)
void(* | post_exec_hook )(struct starpu_task *, unsigned sched_ctx_id)
void(* | do_schedule )(unsigned sched_ctx_id)
void(* | add_workers )(unsigned sched_ctx_id, int *workerids, unsigned nworkers)
void(* | remove_workers )(unsigned sched_ctx_id, int *workerids, unsigned nworkers)
const char * | policy_name
const char * | policy_description
enum starpu_worker_collection_type | worker_type

#### Field Documentation

## ◆ init_sched

void(* starpu_sched_policy::init_sched) (unsigned sched_ctx_id)

Initialize the scheduling policy, called before any other method.

## ◆ deinit_sched

void(* starpu_sched_policy::deinit_sched) (unsigned sched_ctx_id)

Cleanup the scheduling policy

## ◆ push_task

int(* starpu_sched_policy::push_task) (struct starpu_task *)

Insert a task into the scheduler, called when the task becomes ready for execution. This must call starpu_push_task_end() once it has effectively pushed the task to a queue (to note the time when this was done in the task), but before releasing mutexes (so that the task hasn't been already taken by a worker).

## ◆ push_task_notify

void(* starpu_sched_policy::push_task_notify) (struct starpu_task *, int workerid, int perf_workerid, unsigned sched_ctx_id)

Notify the scheduler that a task was pushed on a given worker. This method is called when a task that was explicitly assigned to a worker becomes ready and is about to be executed by the worker. This method therefore permits to keep the state of the scheduler coherent even when StarPU bypasses the scheduling strategy.

## ◆ pop_task

struct starpu_task *(* starpu_sched_policy::pop_task) (unsigned sched_ctx_id)

Get a task from the scheduler. If this method returns NULL, the worker will start sleeping. If later on some task are pushed for this worker, starpu_wake_worker() must be called to wake the worker so it can call the pop_task() method again. The mutex associated to the worker is already taken when this method is called. This method may release it (e.g. for scalability reasons when doing work stealing), but it must acquire it again before taking the decision whether to return a task or NULL, so the atomicity of deciding to return NULL and making the worker actually sleep is preserved. Otherwise in simgrid or blocking driver mode the worker might start sleeping while a task has just been pushed for it. If this method is defined as `NULL`, the worker will only execute tasks from its local queue. In this case, the push_task method should use the starpu_push_local_task method to assign tasks to the different workers.

## ◆ pop_every_task

struct starpu_task *(* starpu_sched_policy::pop_every_task) (unsigned sched_ctx_id)

Remove all available tasks from the scheduler (tasks are chained by the means of the field starpu_task::prev and starpu_task::next). The mutex associated to the worker is already taken when this method is called. This is currently not used and can be discarded.

## ◆ submit_hook

void(* starpu_sched_policy::submit_hook) (struct starpu_task *task)

Optional field. This method is called when a task is submitted.

## ◆ pre_exec_hook

void(* starpu_sched_policy::pre_exec_hook) (struct starpu_task *, unsigned sched_ctx_id)

Optional field. This method is called every time a task is starting.

## ◆ post_exec_hook

void(* starpu_sched_policy::post_exec_hook) (struct starpu_task *, unsigned sched_ctx_id)

Optional field. This method is called every time a task has been executed.

## ◆ do_schedule

void(* starpu_sched_policy::do_schedule) (unsigned sched_ctx_id)

Optional field. This method is called when it is a good time to start scheduling tasks. This is notably called when the application calls starpu_task_wait_for_all() or starpu_do_schedule() explicitly.

## ◆ add_workers

void(* starpu_sched_policy::add_workers) (unsigned sched_ctx_id, int *workerids, unsigned nworkers)

Initialize scheduling structures corresponding to each worker used by the policy.

## ◆ remove_workers

void(* starpu_sched_policy::remove_workers) (unsigned sched_ctx_id, int *workerids, unsigned nworkers)

Deinitialize scheduling structures corresponding to each worker used by the policy.

## ◆ policy_name

const char* starpu_sched_policy::policy_name

Optional field. Name of the policy.

## ◆ policy_description

const char* starpu_sched_policy::policy_description

Optional field. Human readable description of the policy.

## Macro Definition Documentation

## ◆ STARPU_NMAX_SCHED_CTXS

#define STARPU_NMAX_SCHED_CTXS

Define the maximum number of scheduling contexts managed by StarPU. The default value can be modified at configure by using the option --enable-max-sched-ctxs.

## ◆ STARPU_MAXIMPLEMENTATIONS

#define STARPU_MAXIMPLEMENTATIONS

Define the maximum number of implementations per architecture. The default value can be modified at configure by using the option --enable-maximplementations.

## Function Documentation

## ◆ starpu_sched_get_predefined_policies()

struct starpu_sched_policy ** starpu_sched_get_predefined_policies | ( |  | ) |

Return an `NULL`-terminated array of all the predefined scheduling policies.

## ◆ starpu_worker_get_sched_condition()

void starpu_worker_get_sched_condition | ( | int | workerid,
|  | starpu_pthread_mutex_t ** | sched_mutex,
|  | starpu_pthread_cond_t ** | sched_cond
| ) |  |

When there is no available task for a worker, StarPU blocks this worker on a condition variable. This function specifies which condition variable (and the associated mutex) should be used to block (and to wake up) a worker. Note that multiple workers may use the same condition variable. For instance, in the case of a scheduling strategy with a single task queue, the same condition variable would be used to block and wake up all workers.

## ◆ starpu_sched_get_min_priority()

int starpu_sched_get_min_priority | ( | void |  | ) |

TODO: check if this is correct Return the current minimum priority level supported by the scheduling policy

## ◆ starpu_sched_get_max_priority()

int starpu_sched_get_max_priority | ( | void |  | ) |

TODO: check if this is correct Return the current maximum priority level supported by the scheduling policy

## ◆ starpu_sched_set_min_priority()

int starpu_sched_set_min_priority | ( | int | min_prio | ) |

TODO: check if this is correct Define the minimum task priority level supported by the scheduling policy. The default minimum priority level is the same as the default priority level which is 0 by convention. The application may access that value by calling the function starpu_sched_get_min_priority(). This function should only be called from the initialization method of the scheduling policy, and should not be used directly from the application.

## ◆ starpu_sched_set_max_priority()

int starpu_sched_set_max_priority | ( | int | max_prio | ) |

TODO: check if this is correct Define the maximum priority level supported by the scheduling policy. The default maximum priority level is 1. The application may access that value by calling the function starpu_sched_get_max_priority(). This function should only be called from the initialization method of the scheduling policy, and should not be used directly from the application.

## ◆ starpu_worker_can_execute_task()

int starpu_worker_can_execute_task | ( | unsigned | workerid,
|  | struct starpu_task * | task,
|  | unsigned | nimpl
| ) |  |

Check if the worker specified by workerid can execute the codelet. Schedulers need to call it before assigning a task to a worker, otherwise the task may fail to execute.

## ◆ starpu_worker_can_execute_task_impl()

int starpu_worker_can_execute_task_impl | ( | unsigned | workerid,
|  | struct starpu_task * | task,
|  | unsigned * | impl_mask
| ) |  |

Check if the worker specified by workerid can execute the codelet and return which implementation numbers can be used. Schedulers need to call it before assigning a task to a worker, otherwise the task may fail to execute. This should be preferred rather than calling starpu_worker_can_execute_task() for each and every implementation. It can also be used with `impl_mask == NULL` to check for at least one implementation without determining which.

## ◆ starpu_worker_can_execute_task_first_impl()

int starpu_worker_can_execute_task_first_impl | ( | unsigned | workerid,
|  | struct starpu_task * | task,
|  | unsigned * | nimpl
| ) |  |

Check if the worker specified by workerid can execute the codelet and return the first implementation which can be used. Schedulers need to call it before assigning a task to a worker, otherwise the task may fail to execute. This should be preferred rather than calling starpu_worker_can_execute_task() for each and every implementation. It can also be used with `impl_mask == NULL` to check for at least one implementation without determining which.

## ◆ starpu_push_local_task()

int starpu_push_local_task | ( | int | workerid,
|  | struct starpu_task * | task,
|  | int | back
| ) |  |

The scheduling policy may put tasks directly into a worker’s local queue so that it is not always necessary to create its own queue when the local queue is sufficient. If `back` is not 0, `task` is put at the back of the queue where the worker will pop tasks first. Setting `back` to 0 therefore ensures a FIFO ordering.

## ◆ starpu_push_task_end()

int starpu_push_task_end | ( | struct starpu_task * | task | ) |

Must be called by a scheduler to notify that the given task has just been pushed.

## ◆ starpu_get_prefetch_flag()

int starpu_get_prefetch_flag | ( | void |  | ) |

Whether STARPU_PREFETCH was set

## ◆ starpu_prefetch_task_input_on_node_prio()

int starpu_prefetch_task_input_on_node_prio | ( | struct starpu_task * | task,
|  | unsigned | node,
|  | int | prio
| ) |  |

Prefetch data for a given p task on a given p node with a given priority

## ◆ starpu_prefetch_task_input_on_node()

int starpu_prefetch_task_input_on_node | ( | struct starpu_task * | task,
|  | unsigned | node
| ) |  |

Prefetch data for a given p task on a given p node

## ◆ starpu_idle_prefetch_task_input_on_node_prio()

int starpu_idle_prefetch_task_input_on_node_prio | ( | struct starpu_task * | task,
|  | unsigned | node,
|  | int | prio
| ) |  |

Prefetch data for a given p task on a given p node when the bus is idle with a given priority

## ◆ starpu_idle_prefetch_task_input_on_node()

int starpu_idle_prefetch_task_input_on_node | ( | struct starpu_task * | task,
|  | unsigned | node
| ) |  |

Prefetch data for a given p task on a given p node when the bus is idle

## ◆ starpu_prefetch_task_input_for_prio()

int starpu_prefetch_task_input_for_prio | ( | struct starpu_task * | task,
|  | unsigned | worker,
|  | int | prio
| ) |  |

Prefetch data for a given p task on a given p worker with a given priority

## ◆ starpu_prefetch_task_input_for()

int starpu_prefetch_task_input_for | ( | struct starpu_task * | task,
|  | unsigned | worker
| ) |  |

Prefetch data for a given p task on a given p worker

## ◆ starpu_idle_prefetch_task_input_for_prio()

int starpu_idle_prefetch_task_input_for_prio | ( | struct starpu_task * | task,
|  | unsigned | worker,
|  | int | prio
| ) |  |

Prefetch data for a given p task on a given p worker when the bus is idle with a given priority

## ◆ starpu_idle_prefetch_task_input_for()

int starpu_idle_prefetch_task_input_for | ( | struct starpu_task * | task,
|  | unsigned | worker
| ) |  |

Prefetch data for a given p task on a given p worker when the bus is idle

## ◆ starpu_task_footprint()

uint32_t starpu_task_footprint | ( | struct starpu_perfmodel * | model,
|  | struct starpu_task * | task,
|  | struct starpu_perfmodel_arch * | arch,
|  | unsigned | nimpl
| ) |  |

Return the footprint for a given task, taking into account user-provided perfmodel footprint or size_base functions.

## ◆ starpu_task_data_footprint()

uint32_t starpu_task_data_footprint | ( | struct starpu_task * | task | ) |

Return the raw footprint for the data of a given task (without taking into account user-provided functions).

## ◆ starpu_task_expected_length()

double starpu_task_expected_length | ( | struct starpu_task * | task,
|  | struct starpu_perfmodel_arch * | arch,
|  | unsigned | nimpl
| ) |  |

Return expected task duration in micro-seconds.

## ◆ starpu_worker_get_relative_speedup()

double starpu_worker_get_relative_speedup | ( | struct starpu_perfmodel_arch * | perf_arch | ) |

Return an estimated speedup factor relative to CPU speed

## ◆ starpu_task_expected_data_transfer_time()

double starpu_task_expected_data_transfer_time | ( | unsigned | memory_node,
|  | struct starpu_task * | task
| ) |  |

Return expected data transfer time in micro-seconds for the given `memory_node`. Prefer using starpu_task_expected_data_transfer_time_for() which is more precise.

## ◆ starpu_task_expected_data_transfer_time_for()

double starpu_task_expected_data_transfer_time_for | ( | struct starpu_task * | task,
|  | unsigned | worker
| ) |  |

Return expected data transfer time in micro-seconds for the given `worker`.

## ◆ starpu_data_expected_transfer_time()

double starpu_data_expected_transfer_time | ( | starpu_data_handle_t | handle,
|  | unsigned | memory_node,
|  | enum starpu_data_access_mode | mode
| ) |  |

Predict the transfer time (in micro-seconds) to move `handle` to a memory node

## ◆ starpu_task_expected_energy()

double starpu_task_expected_energy | ( | struct starpu_task * | task,
|  | struct starpu_perfmodel_arch * | arch,
|  | unsigned | nimpl
| ) |  |

Return expected energy consumption in J

## ◆ starpu_task_expected_conversion_time()

double starpu_task_expected_conversion_time | ( | struct starpu_task * | task,
|  | struct starpu_perfmodel_arch * | arch,
|  | unsigned | nimpl
| ) |  |

Return expected conversion time in ms (multiformat interface only)

## ◆ starpu_task_notify_ready_soon_register()

void starpu_task_notify_ready_soon_register | ( | starpu_notify_ready_soon_func | f,
|  | void * | data
| ) |  |

Register a callback to be called when it is determined when a task will be ready an estimated amount of time from now, because its last dependency has just started and we know how long it will take.

## ◆ starpu_sched_ctx_worker_shares_tasks_lists()

void starpu_sched_ctx_worker_shares_tasks_lists | ( | int | workerid,
|  | int | sched_ctx_id
| ) |  |

The scheduling policies indicates if the worker may pop tasks from the list of other workers or if there is a central list with task for all the workers

## ◆ starpu_wake_worker_relax()

int starpu_wake_worker_relax | ( | int | workerid | ) |

Wake up `workerid` while temporarily entering the current worker relax state if needed during the waiting process. Return 1 if `workerid` has been woken up or its state_keep_awake flag has been set to `1`, and `0` otherwise (if `workerid` was not in the STATE_SLEEPING or in the STATE_SCHEDULING).

## ◆ starpu_wake_worker_no_relax()

int starpu_wake_worker_no_relax | ( | int | workerid | ) |

Must be called to wake up a worker that is sleeping on the cond. Return 0 whenever the worker is not in a sleeping state or has the state_keep_awake flag on.

## ◆ starpu_wake_worker_locked()

int starpu_wake_worker_locked | ( | int | workerid | ) |

Version of starpu_wake_worker_no_relax() which assumes that the sched mutex is locked

## ◆ starpu_wake_worker_relax_light()

int starpu_wake_worker_relax_light | ( | int | workerid | ) |

Light version of starpu_wake_worker_relax() which, when possible, speculatively set keep_awake on the target worker without waiting for the worker to enter the relax state.