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/*
* idle - task scheduling class .
*
* ( NOTE : these are not related to SCHED_IDLE tasks which are
* handled in sched_fair . c )
*/
/*
* Idle tasks are unconditionally rescheduled :
*/
static void check_preempt_curr_idle ( struct rq * rq , struct task_struct * p )
{
resched_task ( rq - > idle ) ;
}
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static struct task_struct * pick_next_task_idle ( struct rq * rq )
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{
schedstat_inc ( rq , sched_goidle ) ;
return rq - > idle ;
}
/*
* It is not legal to sleep in the idle task - print a warning
* message if some code attempts to do it :
*/
static void
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dequeue_task_idle ( struct rq * rq , struct task_struct * p , int sleep )
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{
spin_unlock_irq ( & rq - > lock ) ;
printk ( KERN_ERR " bad: scheduling from the idle thread! \n " ) ;
dump_stack ( ) ;
spin_lock_irq ( & rq - > lock ) ;
}
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static void put_prev_task_idle ( struct rq * rq , struct task_struct * prev )
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{
}
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# ifdef CONFIG_SMP
sched: simplify move_tasks()
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: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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static unsigned long
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load_balance_idle ( struct rq * this_rq , int this_cpu , struct rq * busiest ,
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unsigned long max_load_move ,
struct sched_domain * sd , enum cpu_idle_type idle ,
int * all_pinned , int * this_best_prio )
{
return 0 ;
}
static int
move_one_task_idle ( struct rq * this_rq , int this_cpu , struct rq * busiest ,
struct sched_domain * sd , enum cpu_idle_type idle )
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{
return 0 ;
}
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# endif
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static void task_tick_idle ( struct rq * rq , struct task_struct * curr )
{
}
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static void set_curr_task_idle ( struct rq * rq )
{
}
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/*
* Simple , special scheduling class for the per - CPU idle tasks :
*/
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const struct sched_class idle_sched_class = {
/* .next is NULL */
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/* no enqueue/yield_task for idle tasks */
/* dequeue is not valid, we print a debug message there: */
. dequeue_task = dequeue_task_idle ,
. check_preempt_curr = check_preempt_curr_idle ,
. pick_next_task = pick_next_task_idle ,
. put_prev_task = put_prev_task_idle ,
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# ifdef CONFIG_SMP
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. load_balance = load_balance_idle ,
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. move_one_task = move_one_task_idle ,
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# endif
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. set_curr_task = set_curr_task_idle ,
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. task_tick = task_tick_idle ,
/* no .task_new for idle tasks */
} ;