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197 lines
5.5 KiB
197 lines
5.5 KiB
/* |
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* Copyright (C) 2014 Freie Universität Berlin |
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* |
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* This file is subject to the terms and conditions of the GNU Lesser |
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* General Public License v2.1. See the file LICENSE in the top level |
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* directory for more details. |
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*/ |
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/** |
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* @defgroup core_sched Scheduler |
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* @ingroup core |
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* @brief The RIOT scheduler |
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* @details |
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* |
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* RIOT features a tickless, preemptive, priority based scheduler. |
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* Context switches can occur either preemptively (i.e. on interrupts), |
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* voluntarily, or when a blocking operation (like `msg_receive()`) is |
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* executed. |
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* Being tickless means it does not have a timer that fires |
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* periodically in order to emulate concurrent execution by switching |
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* threads continuously. |
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* |
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* ## Priorities: |
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* |
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* Every thread is given a priority on creation. The priority values |
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* are "order" or "nice" values, i.e. a higher value means a lower |
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* priority. |
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* |
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* ### Example: |
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* |
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* Given threads with priorities A=6, B=1, and C=3, B has the highest |
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* priority. |
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* |
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* A higher priority means that the scheduler will run this thread |
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* whenever it becomes runnable instead of a thread with a lower |
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* priority. |
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* In case of equal priorities, the threads are scheduled in a |
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* semi-cooperative fashion. That means that unless an interrupt |
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* happens, threads with the same priority will only switch due to |
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* voluntary or implicit context switches. |
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* |
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* ## Interrupts: |
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* |
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* When an interrupt occurs, e.g. because a timer fired or a network |
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* packet was received, the active context is saved and an interrupt |
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* service routine (ISR) that handles the interrupt is executed in |
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* another context. |
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* When the ISR is finished, the `::sched_context_switch_request` flag |
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* can be checked. In case it is set, the `sched_run()` function is |
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* called to determine the next active thread. (In the special case |
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* that the ISR knows that it can not enable a thread switch, this |
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* check can of course be omitted.) |
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* If the flag is not set, the original context is being restored and |
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* the thread resumes immediately. |
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* |
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* ## Voluntary Context Switches: |
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* |
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* There are two function calls that can lead to a voluntary context |
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* switch: `thread_yield()` and `thread_sleep()`. |
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* While the latter disables (think blocks) the thread until it is |
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* woken (think unblocked) again via `thread_wakeup()`, the former only |
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* leads to a context switch in case there is another runnable thread |
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* with at least the same priority. |
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* |
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* ## Implicit Context Switches: |
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* |
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* Some functions that unblock another thread, e.g. `msg_send()` or |
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* `mutex_unlock()`, can cause a thread switch, if the target had a |
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* higher priority. |
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* |
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* |
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* @{ |
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* |
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* @file sched.h |
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* @brief Scheduler API definition |
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* |
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* @author Kaspar Schleiser <kaspar@schleiser.de> |
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*/ |
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#ifndef _SCHEDULER_H |
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#define _SCHEDULER_H |
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#include <stddef.h> |
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#include "bitarithm.h" |
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#include "tcb.h" |
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#include "attributes.h" |
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#include "kernel_types.h" |
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#include "native_sched.h" |
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#ifdef __cplusplus |
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extern "C" { |
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#endif |
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/** |
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* @def SCHED_PRIO_LEVELS |
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* @brief The number of thread priority levels |
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*/ |
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#ifndef SCHED_PRIO_LEVELS |
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#define SCHED_PRIO_LEVELS 16 |
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#endif |
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/** |
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* @brief Triggers the scheduler to schedule the next thread |
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* @returns 1 if sched_active_thread/sched_active_pid was changed, 0 otherwise. |
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*/ |
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int sched_run(void); |
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/** |
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* @brief Set the status of the specified process |
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* |
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* @param[in] process Pointer to the thread control block of the |
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* targeted process |
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* @param[in] status The new status of this thread |
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*/ |
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void sched_set_status(tcb_t *process, unsigned int status); |
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/** |
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* @brief Yield if approriate. |
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* |
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* @details Either yield if other_prio is higher than the current priority, |
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* or if the current thread is not on the runqueue. |
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* |
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* Depending on whether the current execution is in an ISR (inISR()), |
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* thread_yield_higher() is called or @ref sched_context_switch_request is set, |
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* respectively. |
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* |
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* @param[in] other_prio The priority of the target thread. |
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*/ |
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void sched_switch(uint16_t other_prio); |
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/** |
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* @brief Call context switching at thread exit |
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*/ |
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NORETURN void cpu_switch_context_exit(void); |
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/** |
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* Flag indicating whether a context switch is necessary after handling an |
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* interrupt. Supposed to be set in an ISR. |
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*/ |
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extern volatile unsigned int sched_context_switch_request; |
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/** |
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* Thread table |
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*/ |
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extern volatile tcb_t *sched_threads[KERNEL_PID_LAST + 1]; |
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/** |
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* Currently active thread |
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*/ |
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extern volatile tcb_t *sched_active_thread; |
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/** |
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* Number of running (non-terminated) threads |
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*/ |
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extern volatile int sched_num_threads; |
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/** |
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* Process ID of active thread |
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*/ |
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extern volatile kernel_pid_t sched_active_pid; |
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/** |
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* List of runqueues per priority level |
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*/ |
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extern clist_node_t *sched_runqueues[SCHED_PRIO_LEVELS]; |
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#if SCHEDSTATISTICS |
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/** |
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* Scheduler statistics |
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*/ |
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typedef struct { |
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unsigned int laststart; /**< Time stamp of the last time this thread was |
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scheduled to run */ |
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unsigned int schedules; /**< How often the thread was scheduled to run */ |
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unsigned long runtime_ticks; /**< The total runtime of this thread in ticks */ |
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} schedstat; |
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/** |
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* Thread statistics table |
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*/ |
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extern schedstat sched_pidlist[KERNEL_PID_LAST + 1]; |
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/** |
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* @brief Register a callback that will be called on every scheduler run |
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* |
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* @param[in] callback The callback functions the will be called |
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*/ |
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void sched_register_cb(void (*callback)(uint32_t, uint32_t)); |
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#endif |
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#ifdef __cplusplus |
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} |
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#endif |
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#endif // _SCHEDULER_H |
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/** @} */
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