task_struct

 During scheduling, the kernel relies upon a linked list of runnable tasks to determine who should run next. This linked list is a list of data structures of type task_struct that each contain information about a particular task. The important elements in the task_struct from the scheduler's point of view include:

• volatile long state; contains whether this task is runnable, and if not whether it is interruptible (may receive signals) or not.
• long counter; represents the dynamic portion of the task's goodness . Whenever it is reset, it is set to priority. At certain points in the task's execution (most commonly when the 10 msec timer goes off while the task is running) the counter is decremented. If the counter ever reaches 0 while the task is executing, need_resched is set.
• long priority; respresents the static portion of the task's goodness .
• long need_resched; is examined before returning to the current task after a system call and each time the 10 msec timer interrupts. If need_resched is set, schedule() is called.
• unsigned long policy; states whether the current task is being scheduled under soft realtime first in first out (SCHED_FIFO ), soft realtime round robin (SCHED_RR ), or the normal Linux priority scheduling policy (SCHED_OTHER).
• unsigned rt_priority; is used to determine a soft realtime task's goodness .
• struct mm_struct *mm; points to the memory management information for the task. Some tasks share a single mm_struct.