Documentation/scheduler/sched-design-CFS.rst

15 an "ideal, precise multi-tasking CPU" on real hardware.
17 "Ideal multi-tasking CPU" is a (non-existent  :-)) CPU that has 100% physical
20 each at 50% physical power --- i.e., actually in parallel.
25 multi-tasking CPU described above.  In practice, the virtual runtime of a task
33 In CFS the virtual runtime is expressed and tracked via the per-task
34 p->se.vruntime (nanosec-unit) value.  This way, it's possible to accurately
38    p->se.vruntime value --- i.e., tasks would execute simultaneously and no task
41 CFS's task picking logic is based on this p->se.vruntime value and it is thus
42 very simple: it always tries to run the task with the smallest p->se.vruntime
48 with a few add-on embellishments like nice levels, multiprocessing and various
57 runqueues, but it uses a time-ordered rbtree to build a "timeline" of future
61 CFS also maintains the rq->cfs.min_vruntime value, which is a monotonic
68 rq->cfs.load value, which is the sum of the weights of the tasks queued on the
71 CFS maintains a time-ordered rbtree, where all runnable tasks are sorted by the
72 p->se.vruntime key. CFS picks the "leftmost" task from this tree and sticks to it.
74 more and more to the right --- slowly but surely giving a chance for every task
81 p->se.vruntime.  Once p->se.vruntime gets high enough so that another task
82 becomes the "leftmost task" of the time-ordered rbtree it maintains (plus a
84 do not over-schedule tasks and trash the cache), then the new leftmost task is
95 only one central tunable (you have to switch on CONFIG_SCHED_DEBUG):
105 chew.c, ring-test.c, massive_intr.c all work fine and do not impact
112 SMP load-balancing has been reworked/sanitized: the runqueue-walking
113 assumptions are gone from the load-balancing code now, and iterators of the
124   - SCHED_NORMAL (traditionally called SCHED_OTHER): The scheduling
127   - SCHED_BATCH: Does not preempt nearly as often as regular tasks
132   - SCHED_IDLE: This is even weaker than nice 19, but its not a true
139 The command chrt from util-linux-ng 2.13.1.1 can set all of these except
165  - enqueue_task(...)
168    It puts the scheduling entity (task) into the red-black tree and
171  - dequeue_task(...)
174    corresponding scheduling entity out of the red-black tree.  It decrements
177  - yield_task(...)
181    entity at the right-most end of the red-black tree.
183  - check_preempt_curr(...)
188  - pick_next_task(...)
192  - set_curr_task(...)
197  - task_tick(...)
217 CONFIG_RT_GROUP_SCHED permits to group real-time (i.e., SCHED_FIFO and
225    Documentation/admin-guide/cgroup-v1/cgroups.rst for more information about this filesystem.
231 	# mount -t tmpfs cgroup_root /sys/fs/cgroup
233 	# mount -t cgroup -ocpu none /sys/fs/cgroup/cpu