From 4301065920b0cbde3986519582347e883b166f3e Mon Sep 17 00:00:00 2001 From: Peter Williams Date: Thu, 9 Aug 2007 11:16:46 +0200 Subject: 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 Signed-off-by: Ingo Molnar --- kernel/sched_rt.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'kernel/sched_rt.c') diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 002fcf8d3f64..2b0626a43cb8 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -172,15 +172,16 @@ static struct task_struct *load_balance_next_rt(void *arg) return p; } -static int +static unsigned long load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest, unsigned long max_nr_move, unsigned long max_load_move, struct sched_domain *sd, enum cpu_idle_type idle, - int *all_pinned, unsigned long *load_moved) + int *all_pinned) { int this_best_prio, best_prio, best_prio_seen = 0; int nr_moved; struct rq_iterator rt_rq_iterator; + unsigned long load_moved; best_prio = sched_find_first_bit(busiest->rt.active.bitmap); this_best_prio = sched_find_first_bit(this_rq->rt.active.bitmap); @@ -203,11 +204,11 @@ load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest, rt_rq_iterator.arg = busiest; nr_moved = balance_tasks(this_rq, this_cpu, busiest, max_nr_move, - max_load_move, sd, idle, all_pinned, load_moved, + max_load_move, sd, idle, all_pinned, &load_moved, this_best_prio, best_prio, best_prio_seen, &rt_rq_iterator); - return nr_moved; + return load_moved; } static void task_tick_rt(struct rq *rq, struct task_struct *p) -- cgit v1.2.3-55-g7522