At the moment, a lot of load balancing code that is irrelevant to non
SMP systems gets included during non SMP builds.

This patch addresses this issue and reduces the binary size on non
SMP systems:

   text    data     bss     dec     hex filename
  10983      28    1192   12203    2fab sched.o.before
  10739      28    1192   11959    2eb7 sched.o.after
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

At the moment, balance_tasks() provides low level functionality for both
  move_tasks() and move_one_task() (indirectly) via the load_balance()
function (in the sched_class interface) which also provides dual
functionality.  This dual functionality complicates the interfaces and
internal mechanisms and makes the run time overhead of operations that
are called with two run queue locks held.

This patch addresses this issue and reduces the overhead of these
operations.
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Child task may be added on a different cpu that the one on which parent
is running. In which case, task_new_fair() should check whether the new
born task's parent entity should be added as well on the cfs_rq.

Patch below fixes the problem in task_new_fair.

This could fix the put_prev_task_fair() crashes reported.
Reported-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Reported-by: NAndy Whitcroft <apw@shadowen.org>
Signed-off-by: NSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

reintroduce a simplified version of cache-hot/cold scheduling
affinity. This improves performance with certain SMP workloads,
such as sysbench.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

speed up context-switches a bit by not clearing p->exec_start.

(as a side-effect, this also makes p->exec_start a universal timestamp
available to cache-hot estimations.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

do not wakeup-preempt with SCHED_BATCH tasks, their preemption
is batched too, driven by the tick.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

update comment: clarify time-slices and remove obsolete tuning detail.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Prevent wakeup over-scheduling.  Once a task has been preempted by a
task of the same or lower priority, it becomes ineligible for repeated
preemption by same until it has been ticked, or slept.  Instead, the
task is marked for preemption at the next tick.  Tasks of higher
priority still preempt immediately.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Implement feature bit to disable forced preemption. This way
it can be checked whether a workload is overscheduling or not.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The following patch (sched: disable sleeper_fairness on SCHED_BATCH)
seems to break GROUP_SCHED. Although, it may be 'oops'-less due to the
possibility of 'p' being always a valid address.
Signed-off-by: NDmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

disable sleeper fairness for batch tasks - they are about
batch processing after all.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

unit mis-match: wakeup_gran was used against a vruntime
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

noticed by Peter Zijlstra:

fix: move the CPU check into ->task_new_fair(), this way we
can call place_entity() and get child ->vruntime right at
initial wakeup time.

(without this there can be large latencies)
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

noticed by Thomas Gleixner:

cleanup: function prototype cleanups - move into single line
wherever possible.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

cleanup: rename SCHED_FEAT_USE_TREE_AVG to SCHED_FEAT_TREE_AVG, to
make SCHED_FEAT_ names more consistent.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

make dequeue_entity() / enqueue_entity() and update_stats_dequeue() /
update_stats_enqueue() look similar, structure-wise.

zero effect, functionality-wise:

   text    data     bss     dec     hex filename
  34550    3026     100   37676    932c sched.o.before
  34550    3026     100   37676    932c sched.o.after
Signed-off-by: NDmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove obsolete code -- calc_weighted()
Signed-off-by: NDmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

* save ~300 bytes
* activate_idle_task() was moved to avoid a warning

bloat-o-meter output:

add/remove: 6/0 grow/shrink: 0/16 up/down: 438/-733 (-295)		<===
function                                     old     new   delta
__enqueue_entity                               -     165    +165
finish_task_switch                             -     110    +110
update_curr_rt                                 -      79     +79
__load_balance_iterator                        -      32     +32
__task_rq_unlock                               -      28     +28
find_process_by_pid                            -      24     +24
do_sched_setscheduler                        133     123     -10
sys_sched_rr_get_interval                    176     165     -11
sys_sched_getparam                           156     145     -11
normalize_rt_tasks                           482     470     -12
sched_getaffinity                            112      99     -13
sys_sched_getscheduler                        86      72     -14
sched_setaffinity                            226     212     -14
sched_setscheduler                           666     642     -24
load_balance_start_fair                       33       9     -24
load_balance_next_fair                        33       9     -24
dequeue_task_rt                              133      67     -66
put_prev_task_rt                              97      28     -69
schedule_tail                                133      50     -83
schedule                                     682     594     -88
enqueue_entity                               499     366    -133
task_new_fair                                317     180    -137
Signed-off-by: NAlexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

tweak wakeup granularity.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The thing is that __pick_next_entity() must never be called when
first_fair(cfs_rq) == NULL. It wouldn't be a problem, should 'run_node'
be the very first field of 'struct sched_entity' (and it's the second).

The 'nr_running != 0' check is _not_ enough, due to the fact that
'current' is not within the tree. Generic paths are ok (e.g. schedule()
as put_prev_task() is called previously)... I'm more worried about e.g.
migration_call() -> CPU_DEAD_FROZEN -> migrate_dead_tasks()... if
'current' == rq->idle, no problems.. if it's one of the SCHED_NORMAL
tasks (or imagine, some other use-cases in the future -- i.e. we should
not make outer world dependent on internal details of sched_fair class)
-- it may be "Houston, we've got a problem" case.

it's +16 bytes to the ".text". Another variant is to make 'run_node' the
first data member of 'struct sched_entity' but an additional check (se !
= NULL) is still needed in pick_next_entity().
Signed-off-by: NDmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

Make vslice accurate wrt nice levels, and add some comments
while we're at it.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

mark scheduling classes as const. The speeds up the code
a bit and shrinks it:

   text    data     bss     dec     hex filename
  40027    4018     292   44337    ad31 sched.o.before
  40190    3842     292   44324    ad24 sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

There is a possibility that because of task of a group moving from one
cpu to another, it may gain more cpu time that desired. See 
http://marc.info/?l=linux-kernel&m=119073197730334 for details.

This is an attempt to fix that problem. Basically it simulates dequeue
of higher level entities as if they are going to sleep. Similarly it
simulate wakeup of higher level entities as if they are waking up from
sleep.
Signed-off-by: NSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

Recent fix to check_preempt_wakeup() to check for preemption at higher
levels caused a size bloat for !CONFIG_FAIR_GROUP_SCHED.

Fix the problem.

  42277   10598     320   53195    cfcb kernel/sched.o-before_this_patch
  42216   10598     320   53134    cf8e kernel/sched.o-after_this_patch
Signed-off-by: NSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

cleanup, remove stale comment.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

speed up and simplify vslice calculations.

[ From: Mike Galbraith <efault@gmx.de>: build fix ]
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

clean up min_vruntime use.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

fix yield bugs due to the current-not-in-rbtree changes: the task is
not in the rbtree so rbtree-removal is a no-no.

[ From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>: build fix. ]

also, nice code size reduction:

kernel/sched.o:
   text    data     bss     dec     hex filename
  38323    3506      24   41853    a37d sched.o.before
  38236    3506      24   41766    a326 sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NDmitry Adamushko <dmitry.adamushko@gmail.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

group scheduler wakeup latency fix: when checking for preemption
we must check cross-group too, not just intra-group.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Lee Schermerhorn noticed that set_leftmost() contains dead code,
remove this.
Reported-by: NLee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

max_vruntime() simplification.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

fix sign check error in place_entity() - we'd get excessive
latencies due to negatives being converted to large u64's.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

undo some of the recent changes that are not needed after all,
such as last_min_vruntime.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

remove last_min_vruntime use - prepare to remove it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

entity_key() fix - we'd occasionally end up with a 0 vruntime
in the !initial case.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

debug feature: check how well we schedule within a reasonable
vruntime 'spread' range. (note that CPU overload can increase
the spread, so this is not a hard condition, but normal loads
should be within the spread.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>

add vslice: the load-dependent "virtual slice" a task should
run ideally, so that the observed latency stays within the
sched_latency window.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

remove unneeded tunables.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

With the view of supporting user-id based fair scheduling (and not just
container-based fair scheduling), this patch renames several functions
and makes them independent of whether they are being used for container
or user-id based fair scheduling.

Also fix a problem reported by KAMEZAWA Hiroyuki (wrt allocating
less-sized array for tg->cfs_rq[] and tf->se[]).
Signed-off-by: NSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: NDhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

- Print &rq->cfs statistics as well (useful for group scheduling)
Signed-off-by: NSrivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: NDhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>