On Tue, Apr 25, 2006 at 01:08:00PM +1000, Peter Williams wrote:
> 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.
>
> This patch is on top of
> sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks.patch
>
> Signed-off-by: Peter Williams <[email protected]>
>
> --
> Peter Williams [email protected]
>
> "Learning, n. The kind of ignorance distinguishing the studious."
> -- Ambrose Bierce
> Index: MM-2.6.17-rc1-mm3/kernel/sched.c
> ===================================================================
> --- MM-2.6.17-rc1-mm3.orig/kernel/sched.c 2006-04-25 12:53:39.000000000 +1000
> +++ MM-2.6.17-rc1-mm3/kernel/sched.c 2006-04-25 12:56:14.000000000 +1000
> @@ -2059,7 +2059,10 @@ 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;
>
> @@ -2108,9 +2111,10 @@ 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;
I think we need to change this to
if (skip_for_load && idx < this_best_prio && idx == busiest_best_prio)
skip_for_load = !busiest_best_prio_seen;
Otherwise we will reset skip_for_load to '0' even for the tasks whose prio is
less than this_best_prio but not equal to 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++;
> @@ -2133,8 +2137,6 @@ 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++;
-
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