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SubjectRe: [PATCH] sched: Fix boolean expression in move_tasks()
Andrew Morton wrote:
> Peter Williams <pwil3058@bigpond.net.au> wrote:
>> Negate the expression and apply de Marcos rule to simplify it. This
>> patch is on top of
>> sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks.patch
>>
>> Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
>>
>> --
>> Peter Williams pwil3058@bigpond.net.au
>>
>> "Learning, n. The kind of ignorance distinguishing the studious."
>> -- Ambrose Bierce
>>
>>
>> [smpnice-fix-boolean-expression text/plain (824 bytes)]
>> Index: MM-2.6.17-rc1-mm3/kernel/sched.c
>> ===================================================================
>> --- MM-2.6.17-rc1-mm3.orig/kernel/sched.c 2006-04-21 12:26:54.000000000 +1000
>> +++ MM-2.6.17-rc1-mm3/kernel/sched.c 2006-04-25 09:09:54.000000000 +1000
>> @@ -2108,7 +2108,7 @@ 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;
>
> But Suresh's
> sched-avoid-unnecessarily-moving-highest-priority-task-move_tasks-fix.patch
> changed all this code:
>
> /*
> * To help distribute high priority tasks accross CPUs we don't
> * skip a task if it will be the highest priority task (i.e. smallest
> * prio value) on its new queue regardless of its load weight
> */
> skip_for_load = tmp->load_weight > rem_load_move;
> if (skip_for_load && idx < this_best_prio && idx == busiest_best_prio)
> skip_for_load = !busiest_best_prio_seen &&
> head->next == head->prev;
> if (skip_for_load ||
> !can_migrate_task(tmp, busiest, this_cpu, sd, idle, &pinned)) {
> if (curr != head)
> goto skip_queue;
> idx++;
> goto skip_bitmap;
> }
>
>
> What to do?

Suresh's patch was wrong and this was intended as an alternative.
Unfortunately, it is also in adequate and the setting of
busiest_best_prio_seen needs to be moved to just after skip_for_load is
set. I have another patch that does that (and adds to the comments).
Should I send that separately or roll the two patches together?

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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