starpu-max/doc/doxygen/chapters/api/scheduling_policy.doxy

/*
 * This file is part of the StarPU Handbook.
 * Copyright (C) 2009--2011  Universit@'e de Bordeaux
 * Copyright (C) 2010, 2011, 2012, 2013, 2014, 2016, 2017  CNRS
 * Copyright (C) 2011, 2012 INRIA
 * See the file version.doxy for copying conditions.
 */

/*! \defgroup API_Scheduling_Policy Scheduling Policy

\brief TODO. While StarPU comes with a variety of scheduling policies
(see \ref TaskSchedulingPolicy), 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.

\def STARPU_MAXIMPLEMENTATIONS
\ingroup API_Scheduling_Policy
Define the maximum number of implementations per architecture. The default value can be modified at
configure by using the option \ref enable-maximplementations "--enable-maximplementations".

\struct starpu_sched_policy
\ingroup API_Scheduling_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:

<ul>
<li>starpu_sched_policy::submit_hook when the task is submitted</li>
<li>starpu_sched_policy::push_task when the task becomes ready. The scheduler is here <b>given</b> the task</li>
<li>starpu_sched_policy::pop_task when the worker is idle. The scheduler here <b>gives</b> back the task to the core</li>
<li>starpu_sched_policy::pre_exec_hook right before the worker actually starts the task computation (after transferring any missing data).</li>
<li>starpu_sched_policy::post_exec_hook right after the worker actually completes the task computation.</li>
</ul>

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

<ul>
<li>starpu_sched_policy::submit_hook when the task is submitted</li>
<li>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.</li>
<li>starpu_sched_policy::pre_exec_hook right before the worker actually starts the task computation (after transferring any missing data).</li>
<li>starpu_sched_policy::post_exec_hook right after the worker actually completes the task computation.</li>
</ul>


\var void (*starpu_sched_policy::init_sched)(unsigned sched_ctx_id)
        Initialize the scheduling policy, called before any other method.
\var void (*starpu_sched_policy::deinit_sched)(unsigned sched_ctx_id)
        Cleanup the scheduling policy, called before any other method.
\var int (*starpu_sched_policy::push_task)(struct starpu_task *)
        Insert a task into the scheduler, called when the task becomes ready for
        execution.
\var 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.
\var 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 <c>NULL</c>, 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.
\var 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.
\var void (*starpu_sched_policy::submit_hook)(struct starpu_task *)
        Optional field. This method is called when a task is submitted.
\var void (*starpu_sched_policy::pre_exec_hook)(struct starpu_task *)
        Optional field. This method is called every time a task is starting.
\var void (*starpu_sched_policy::post_exec_hook)(struct starpu_task *)
        Optional field. This method is called every time a task has been executed.
\var 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.
\var 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.
\var 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.
\var const char *starpu_sched_policy::policy_name
        Optional field. Name of the policy.
\var const char *starpu_sched_policy::policy_description
        Optional field. Human readable description of the policy.

\fn struct starpu_sched_policy **starpu_sched_get_predefined_policies()
\ingroup API_Scheduling_Policy
Return an <c>NULL</c>-terminated array of all the predefined scheduling
policies.

\fn void starpu_worker_get_sched_condition(int workerid, starpu_pthread_mutex_t **sched_mutex, starpu_pthread_cond_t **sched_cond)
\ingroup API_Scheduling_Policy
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.

\fn int starpu_wake_worker_no_relax(int workerid)
\ingroup API_Scheduling_Policy
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.

\fn int starpu_wake_worker_locked(int workerid)
\ingroup API_Scheduling_Policy
Version of starpu_wake_worker_no_relax() which assumes that the sched
mutex is locked

\fn int starpu_sched_set_min_priority(int min_prio)
\ingroup API_Scheduling_Policy
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.

\fn int starpu_sched_set_max_priority(int max_prio)
\ingroup API_Scheduling_Policy
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.

\fn int starpu_sched_get_min_priority(void)
\ingroup API_Scheduling_Policy
TODO: check if this is correct
Return the current minimum priority level supported by the scheduling
policy

\fn int starpu_sched_get_max_priority(void)
\ingroup API_Scheduling_Policy
TODO: check if this is correct
Return the current maximum priority level supported by the scheduling
policy

\fn int starpu_push_local_task(int workerid, struct starpu_task *task, int back)
\ingroup API_Scheduling_Policy
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 \p back is not 0, \p task is put
at the back of the queue where the worker will pop tasks first.
Setting \p back to 0 therefore ensures a FIFO ordering.

\fn int starpu_push_task_end(struct starpu_task *task)
\ingroup API_Scheduling_Policy
Must be called by a scheduler to notify that the given
task has just been pushed.

\fn int starpu_worker_can_execute_task(unsigned workerid, struct starpu_task *task, unsigned nimpl)
\ingroup API_Scheduling_Policy
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.

\fn int starpu_worker_can_execute_task_impl(unsigned workerid, struct starpu_task *task, unsigned *impl_mask)
\ingroup API_Scheduling_Policy
Check if the worker specified by workerid can execute the codelet and returns
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 <c>impl_mask == NULL</c> to
check for at least one implementation without determining which.

\fn int starpu_worker_can_execute_task_first_impl(unsigned workerid, struct starpu_task *task, unsigned *nimpl)
\ingroup API_Scheduling_Policy
Check if the worker specified by workerid can execute the codelet and returns
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 <c>impl_mask == NULL</c> to
check for at least one implementation without determining which.

\fn uint32_t starpu_task_footprint(struct starpu_perfmodel *model, struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
\ingroup API_Scheduling_Policy
Return the footprint for a given task, taking into account user-provided
perfmodel footprint or size_base functions.

\fn uint32_t starpu_task_data_footprint(struct starpu_task *task)
\ingroup API_Scheduling_Policy
Return the raw footprint for the data of a given task (without taking into account user-provided functions).

\fn double starpu_task_expected_length(struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
\ingroup API_Scheduling_Policy
Return expected task duration in micro-seconds.

\fn double starpu_worker_get_relative_speedup(struct starpu_perfmodel_arch *perf_arch)
\ingroup API_Scheduling_Policy
Return an estimated speedup factor relative to CPU speed

\fn double starpu_task_expected_data_transfer_time(unsigned memory_node, struct starpu_task *task)
\ingroup API_Scheduling_Policy
Return expected data transfer time in micro-seconds.

\fn double starpu_data_expected_transfer_time(starpu_data_handle_t handle, unsigned memory_node, enum starpu_data_access_mode mode)
\ingroup API_Scheduling_Policy
Predict the transfer time (in micro-seconds) to move \p handle to a memory node

\fn double starpu_task_expected_energy(struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
\ingroup API_Scheduling_Policy
Return expected energy consumption in J

\fn double starpu_task_expected_conversion_time(struct starpu_task *task, struct starpu_perfmodel_arch *arch, unsigned nimpl)
\ingroup API_Scheduling_Policy
Return expected conversion time in ms (multiformat interface only)

\fn int starpu_get_prefetch_flag(void)
\ingroup API_Scheduling_Policy
Whether \ref STARPU_PREFETCH was set

\fn int starpu_prefetch_task_input_on_node(struct starpu_task *task, unsigned node)
\ingroup API_Scheduling_Policy
Prefetch data for a given task on a given node

\fn int starpu_idle_prefetch_task_input_on_node(struct starpu_task *task, unsigned node)
\ingroup API_Scheduling_Policy
Prefetch data for a given task on a given node when the bus is idle

\fn void starpu_sched_ctx_worker_shares_tasks_lists(int workerid, int sched_ctx_id)
\ingroup API_Scheduling_Policy
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

*/