1 files changed, 126 insertions, 0 deletions
diff --git a/Documentation/scheduler/sched-coding.txt b/Documentation/scheduler/sched-coding.txt
new file mode 100644
index 0000000..cbd8db7
--- /dev/null
+++ b/Documentation/scheduler/sched-coding.txt
@@ -0,0 +1,126 @@
+     Reference for various scheduler-related methods in the O(1) scheduler
+		Robert Love <rml@tech9.net>, MontaVista Software
+
+
+Note most of these methods are local to kernel/sched.c - this is by design.
+The scheduler is meant to be self-contained and abstracted away.  This document
+is primarily for understanding the scheduler, not interfacing to it.  Some of
+the discussed interfaces, however, are general process/scheduling methods.
+They are typically defined in include/linux/sched.h.
+
+
+Main Scheduling Methods
+-----------------------
+
+void load_balance(runqueue_t *this_rq, int idle)
+	Attempts to pull tasks from one cpu to another to balance cpu usage,
+	if needed.  This method is called explicitly if the runqueues are
+	imbalanced or periodically by the timer tick.  Prior to calling,
+	the current runqueue must be locked and interrupts disabled.
+
+void schedule()
+	The main scheduling function.  Upon return, the highest priority
+	process will be active.
+
+
+Locking
+-------
+
+Each runqueue has its own lock, rq->lock.  When multiple runqueues need
+to be locked, lock acquires must be ordered by ascending &runqueue value.
+
+A specific runqueue is locked via
+
+	task_rq_lock(task_t pid, unsigned long *flags)
+
+which disables preemption, disables interrupts, and locks the runqueue pid is
+running on.  Likewise,
+
+	task_rq_unlock(task_t pid, unsigned long *flags)
+
+unlocks the runqueue pid is running on, restores interrupts to their previous
+state, and reenables preemption.
+
+The routines
+
+	double_rq_lock(runqueue_t *rq1, runqueue_t *rq2)
+
+and
+
+	double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
+
+safely lock and unlock, respectively, the two specified runqueues.  They do
+not, however, disable and restore interrupts.  Users are required to do so
+manually before and after calls.
+
+
+Values
+------
+
+MAX_PRIO
+	The maximum priority of the system, stored in the task as task->prio.
+	Lower priorities are higher.  Normal (non-RT) priorities range from
+	MAX_RT_PRIO to (MAX_PRIO - 1).
+MAX_RT_PRIO
+	The maximum real-time priority of the system.  Valid RT priorities
+	range from 0 to (MAX_RT_PRIO - 1).
+MAX_USER_RT_PRIO
+	The maximum real-time priority that is exported to user-space.  Should
+	always be equal to or less than MAX_RT_PRIO.  Setting it less allows
+	kernel threads to have higher priorities than any user-space task.
+MIN_TIMESLICE
+MAX_TIMESLICE
+	Respectively, the minimum and maximum timeslices (quanta) of a process.
+
+Data
+----
+
+struct runqueue
+	The main per-CPU runqueue data structure.
+struct task_struct
+	The main per-process data structure.
+
+
+General Methods
+---------------
+
+cpu_rq(cpu)
+	Returns the runqueue of the specified cpu.
+this_rq()
+	Returns the runqueue of the current cpu.
+task_rq(pid)
+	Returns the runqueue which holds the specified pid.
+cpu_curr(cpu)
+	Returns the task currently running on the given cpu.
+rt_task(pid)
+	Returns true if pid is real-time, false if not.
+
+
+Process Control Methods
+-----------------------
+
+void set_user_nice(task_t *p, long nice)
+	Sets the "nice" value of task p to the given value.
+int setscheduler(pid_t pid, int policy, struct sched_param *param)
+	Sets the scheduling policy and parameters for the given pid.
+int set_cpus_allowed(task_t *p, unsigned long new_mask)
+	Sets a given task's CPU affinity and migrates it to a proper cpu.
+	Callers must have a valid reference to the task and assure the
+	task not exit prematurely.  No locks can be held during the call.
+set_task_state(tsk, state_value)
+	Sets the given task's state to the given value.
+set_current_state(state_value)
+	Sets the current task's state to the given value.
+void set_tsk_need_resched(struct task_struct *tsk)
+	Sets need_resched in the given task.
+void clear_tsk_need_resched(struct task_struct *tsk)
+	Clears need_resched in the given task.
+void set_need_resched()
+	Sets need_resched in the current task.
+void clear_need_resched()
+	Clears need_resched in the current task.
+int need_resched()
+	Returns true if need_resched is set in the current task, false
+	otherwise.
+yield()
+	Place the current process at the end of the runqueue and call schedule.