round a tiny bit better in high-frequency rescheduling scenarios,
by rounding around zero instead of rounding down.

(this is pretty theoretical though)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

do small deltas in the weight and multiplication constant table so
that the worst-case numeric error is better than 1:100000000. (8 digits)

the current error table is:

     nice       mult *   inv_mult   error
     ------------------------------------------
     -20:      88761 *      48388  -0.0000000065
     -19:      71755 *      59856  -0.0000000037
     -18:      56483 *      76040   0.0000000056
     -17:      46273 *      92818   0.0000000042
     -16:      36291 *     118348  -0.0000000065
     -15:      29154 *     147320  -0.0000000037
     -14:      23254 *     184698  -0.0000000009
     -13:      18705 *     229616  -0.0000000037
     -12:      14949 *     287308  -0.0000000009
     -11:      11916 *     360437  -0.0000000009
     -10:       9548 *     449829  -0.0000000009
      -9:       7620 *     563644  -0.0000000037
      -8:       6100 *     704093   0.0000000009
      -7:       4904 *     875809   0.0000000093
      -6:       3906 *    1099582  -0.0000000009
      -5:       3121 *    1376151  -0.0000000058
      -4:       2501 *    1717300   0.0000000009
      -3:       1991 *    2157191  -0.0000000035
      -2:       1586 *    2708050   0.0000000009
      -1:       1277 *    3363326   0.0000000014
       0:       1024 *    4194304   0.0000000000
       1:        820 *    5237765   0.0000000009
       2:        655 *    6557202   0.0000000033
       3:        526 *    8165337  -0.0000000079
       4:        423 *   10153587   0.0000000012
       5:        335 *   12820798   0.0000000079
       6:        272 *   15790321   0.0000000037
       7:        215 *   19976592  -0.0000000037
       8:        172 *   24970740  -0.0000000037
       9:        137 *   31350126  -0.0000000079
      10:        110 *   39045157  -0.0000000061
      11:         87 *   49367440  -0.0000000037
      12:         70 *   61356676   0.0000000056
      13:         56 *   76695844  -0.0000000075
      14:         45 *   95443717  -0.0000000072
      15:         36 *  119304647  -0.0000000009
      16:         29 *  148102320  -0.0000000037
      17:         23 *  186737708  -0.0000000028
      18:         18 *  238609294  -0.0000000009
      19:         15 *  286331153  -0.0000000002
Signed-off-by: NIngo Molnar <mingo@elte.hu>

optimize update_rq_clock() calls in the load-balancer: update them
right after locking the runqueue(s) so that the pull functions do
not have to call it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

optimize activate_task() by removing update_rq_clock() from it.
(and add update_rq_clock() to all callsites of activate_task() that
did not have it before.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

move the __update_rq_clock() call from update_cpu_load() to
scheduler_tick().

( identity transformation that causes no change in functionality. )

this allows the direct use of rq->clock in ->task_tick() functions.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

final step: remove all (now superfluous) 'u64 now' variables.

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from deactivate_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from dequeue_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from enqueue_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from dec_nr_running().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from inc_nr_running().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from dec_load().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from inc_load().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from update_curr_load().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from ->task_new().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from ->put_prev_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from pick_next_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from ->pick_next_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from ->dequeue_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the 'u64 now' parameter from ->enqueue_task().

( identity transformation that causes no change in functionality. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

change all 'now' timestamp uses in assignments to rq->clock.

( this is an identity transformation that causes no functionality change:
  all such new rq->clock is necessarily preceded by an update_rq_clock()
  call. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the (now unused) __rq_clock() function.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

eliminate __rq_clock() use by changing it to:

   __update_rq_clock(rq)
   now = rq->clock;

identity transformation - no change in behavior.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

remove the now unused rq_clock() function.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

eliminate rq_clock() use by changing it to:

   update_rq_clock(rq)
   now = rq->clock;

identity transformation - no change in behavior.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

add the [__]update_rq_clock(rq) functions. (No change in functionality,
just reorganization to prepare for elimination of the heavy 64-bit
timestamp-passing in the scheduler.)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

There are two problems with balance_tasks() and how it used:

1. The variables best_prio and best_prio_seen (inherited from the old
move_tasks()) were only required to handle problems caused by the
active/expired arrays, the order in which they were processed and the
possibility that the task with the highest priority could be on either.
  These issues are no longer present and the extra overhead associated
with their use is unnecessary (and possibly wrong).

2. In the absence of CONFIG_FAIR_GROUP_SCHED being set, the same
this_best_prio variable needs to be used by all scheduling classes or
there is a risk of moving too much load.  E.g. if the highest priority
task on this at the beginning is a fairly low priority task and the rt
class migrates a task (during its turn) then that moved task becomes the
new highest priority task on this_rq but when the sched_fair class
initializes its copy of this_best_prio it will get the priority of the
original highest priority task as, due to the run queue locks being
held, the reschedule triggered by pull_task() will not have taken place.
  This could result in inappropriate overriding of skip_for_load and
excessive load being moved.

The attached patch addresses these problems by deleting all reference to
best_prio and best_prio_seen and making this_best_prio a reference
parameter to the various functions involved.

load_balance_fair() has also been modified so that this_best_prio is
only reset (in the loop) if CONFIG_FAIR_GROUP_SCHED is set.  This should
preserve the effect of helping spread groups' higher priority tasks
around the available CPUs while improving system performance when
CONFIG_FAIR_GROUP_SCHED isn't set.
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel.sched_domain hierarchy is under CTL_UNNUMBERED and thus
unreachable to sysctl(2). Generating .ctl_number's in such situation is
not useful.
Signed-off-by: NAlexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

speed up schedule(): share the 'now' parameter that deactivate_task()
was calculating internally.

( this also fixes the small accounting window between the deactivate
  call and the pick_next_task() call. )
Signed-off-by: NIngo Molnar <mingo@elte.hu>

uninline rq_clock() to save 263 bytes of code:

   text    data     bss     dec     hex filename
   39561    3642      24   43227    a8db sched.o.before
   39298    3642      24   42964    a7d4 sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>

here's another tiny cleanup.  The generated code is not affected (gcc is
smart enough) but for people looking over the code it is just irritating
to have the extra conditional.
Signed-off-by: NUlrich Drepper <drepper@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The move_tasks() function is currently multiplexed with two distinct
capabilities:

1. attempt to move a specified amount of weighted load from one run
queue to another; and
2. attempt to move a specified number of tasks from one run queue to
another.

The first of these capabilities is used in two places, load_balance()
and load_balance_idle(), and in both of these cases the return value of
move_tasks() is used purely to decide if tasks/load were moved and no
notice of the actual number of tasks moved is taken.

The second capability is used in exactly one place,
active_load_balance(), to attempt to move exactly one task and, as
before, the return value is only used as an indicator of success or failure.

This multiplexing of sched_task() was introduced, by me, as part of the
smpnice patches and was motivated by the fact that the alternative, one
function to move specified load and one to move a single task, would
have led to two functions of roughly the same complexity as the old
move_tasks() (or the new balance_tasks()).  However, the new modular
design of the new CFS scheduler allows a simpler solution to be adopted
and this patch addresses that solution by:

1. adding a new function, move_one_task(), to be used by
active_load_balance(); and
2. making move_tasks() a single purpose function that tries to move a
specified weighted load and returns 1 for success and 0 for failure.

One of the consequences of these changes is that neither move_one_task()
or the new move_tasks() care how many tasks sched_class.load_balance()
moves and this enables its interface to be simplified by returning the
amount of load moved as its result and removing the load_moved pointer
from the argument list.  This helps simplify the new move_tasks() and
slightly reduces the amount of work done in each of
sched_class.load_balance()'s implementations.

Further simplification, e.g. changes to balance_tasks(), are possible
but (slightly) complicated by the special needs of load_balance_fair()
so I've left them to a later patch (if this one gets accepted).

NB Since move_tasks() gets called with two run queue locks held even
small reductions in overhead are worthwhile.

[ mingo@elte.hu ]

this change also reduces code size nicely:

   text    data     bss     dec     hex filename
   39216    3618      24   42858    a76a sched.o.before
   39173    3618      24   42815    a73f sched.o.after
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Peter Williams suggested to flip the order of update_cpu_load(rq) with
the ->task_tick() call. This is a NOP for the current scheduler (the
two functions are independent of each other), ->task_tick() might
create some state for update_cpu_load() in the future (or in PlugSched).
Signed-off-by: NIngo Molnar <mingo@elte.hu>

move the rest of the debugging/instrumentation code to under
CONFIG_SCHEDSTATS too. This reduces code size and speeds code up:

    text    data     bss     dec     hex filename
   33044    4122      28   37194    914a sched.o.before
   32708    4122      28   36858    8ffa sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>

move load-calculation functions so that they can use the per-policy
declarations and methods.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

make sched_class.task_new == NULL a 'default method', this
allows the removal of task_rt_new.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

uninline inc_nr_running() and dec_nr_running():

   text    data     bss     dec     hex filename
   29039    4162      24   33225    81c9 sched.o.before
   29027    4162      24   33213    81bd sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>

uninline calc_delta_mine():

   text    data     bss     dec     hex filename
   29162    4162      24   33348    8244 sched.o.before
   29039    4162      24   33225    81c9 sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>

use fixed limit in calc_delta_mine() - this saves an instruction :)
Signed-off-by: NIngo Molnar <mingo@elte.hu>

1. The only place that RTPRIO_TO_LOAD_WEIGHT() is used is in the call to
move_tasks() in the function active_load_balance() and its purpose here
is just to make sure that the load to be moved is big enough to ensure
that exactly one task is moved (if there's one available).  This can be
accomplished by using ULONG_MAX instead and this allows
RTPRIO_TO_LOAD_WEIGHT() to be deleted.

2. This, in turn, allows PRIO_TO_LOAD_WEIGHT() to be deleted.

3. This allows load_weight() to be deleted which allows
TIME_SLICE_NICE_ZERO to be deleted along with the comment above it.
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>