From: Peter Williams Problem: In the patch sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks.patch I got a the sense of a boolean expression wrong when assigning a value to skip_for_load. The expression should have been negated before being assigned. Additionally, busiest_best_prio_seen is being set when tasks are moved instead of when they are skipped which will cause problems when the current task does not have prio=busiest_best_prio. Solution: Negate the expression and apply de Marcos rule to simplify it and move the setting of busiest_best_prio_seen. Signed-off-by: Peter Williams Cc: "Siddha, Suresh B" Cc: Ingo Molnar Signed-off-by: Andrew Morton --- kernel/sched.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff -puN kernel/sched.c~sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks-fix-2 kernel/sched.c --- devel/kernel/sched.c~sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks-fix-2 2006-06-09 15:22:30.000000000 -0700 +++ devel-akpm/kernel/sched.c 2006-06-09 15:22:30.000000000 -0700 @@ -1998,7 +1998,10 @@ static int move_tasks(runqueue_t *this_r busiest_best_prio = rq_best_prio(busiest); /* * Enable handling of the case where there is more than one task - * with the best priority. + * with the best priority. If the current running task is one + * of those with prio==busiest_best_prio we know it won't be moved + * and therefore it's safe to override the skip (based on load) of + * any task we find with that prio. */ busiest_best_prio_seen = busiest_best_prio == busiest->curr->prio; @@ -2047,9 +2050,10 @@ skip_queue: */ skip_for_load = tmp->load_weight > rem_load_move; if (skip_for_load && idx < this_best_prio) - skip_for_load = busiest_best_prio_seen || idx != busiest_best_prio; + skip_for_load = !busiest_best_prio_seen && idx == busiest_best_prio; if (skip_for_load || !can_migrate_task(tmp, busiest, this_cpu, sd, idle, &pinned)) { + busiest_best_prio_seen |= idx == busiest_best_prio; if (curr != head) goto skip_queue; idx++; @@ -2072,8 +2076,6 @@ skip_queue: if (pulled < max_nr_move && rem_load_move > 0) { if (idx < this_best_prio) this_best_prio = idx; - if (idx == busiest_best_prio) - busiest_best_prio_seen = 1; if (curr != head) goto skip_queue; idx++; _