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_fair.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'kernel/sched_fair.c') diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 9f40158..7307a37 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -944,11 +944,11 @@ static int cfs_rq_best_prio(struct cfs_rq *cfs_rq) return p->prio; } -static int +static unsigned long load_balance_fair(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 *total_load_moved) + int *all_pinned) { struct cfs_rq *busy_cfs_rq; unsigned long load_moved, total_nr_moved = 0, nr_moved; @@ -1006,9 +1006,7 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest, break; } - *total_load_moved = max_load_move - rem_load_move; - - return total_nr_moved; + return max_load_move - rem_load_move; } /* -- cgit v1.1