Siddha, Suresh B wrote:
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.
And why is that a problem? The intention of this code is to make sure
at least one busiest_best_prio task doesn't get moved as a result of the
"skip for reasons of load weight" mechanism being overridden by the "idx
< this_best_prio" exception. I can't see how this intention is being
subverted.
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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