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2007-08-24sched: optimize task_tick_rt() a bitDmitry Adamushko
Mitchell Erblich suggested a quality-of-implementation change to not requeue SCHED_RR tasks if there's only a single task on the runqueue, by checking for rq->nr_running == 1. provide a more efficient implementation of that, to check that particular RT priority-queue only. [ From: mingo@elte.hu ] Also first requeue the task then set need_resched - results in slightly better machine-instruction ordering. Also clean up the code a bit. Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove the 'u64 now' parameter from ->put_prev_task()Ingo Molnar
remove the 'u64 now' parameter from ->put_prev_task(). ( identity transformation that causes no change in functionality. ) Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove the 'u64 now' parameter from ->pick_next_task()Ingo Molnar
remove the 'u64 now' parameter from ->pick_next_task(). ( identity transformation that causes no change in functionality. ) Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove the 'u64 now' parameter from ->dequeue_task()Ingo Molnar
remove the 'u64 now' parameter from ->dequeue_task(). ( identity transformation that causes no change in functionality. ) Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove the 'u64 now' parameter from ->enqueue_task()Ingo Molnar
remove the 'u64 now' parameter from ->enqueue_task(). ( identity transformation that causes no change in functionality. ) Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove the 'u64 now' parameter from update_curr_rt()Ingo Molnar
remove the 'u64 now' parameter from update_curr_rt(). ( identity transformation that causes no change in functionality. ) Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: remove 'now' use from assignmentsIngo Molnar
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: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: fix bug in balance_tasks()Peter Williams
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: Peter Williams <pwil3058@bigpond.net.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-08-09sched: simplify move_tasks()Peter Williams
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>
2007-08-02[PATCH] sched: reduce debug codeIngo Molnar
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: Ingo Molnar <mingo@elte.hu>
2007-08-02[PATCH] sched: ->task_new cleanupIngo Molnar
make sched_class.task_new == NULL a 'default method', this allows the removal of task_rt_new. Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-07-09sched: cfs core, kernel/sched_rt.cIngo Molnar
add kernel/sched_rt.c: SCHED_FIFO/SCHED_RR support. The behavior and semantics of SCHED_FIFO/SCHED_RR tasks is unchanged. Signed-off-by: Ingo Molnar <mingo@elte.hu>