Re: [PATCH] sched: Fix boolean expression in move_tasks()

[Peter Williams]

Andrew Morton wrote:
> Peter Williams <pwil3058@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> >
> >  -- 
> >  Peter Williams                                   pwil3058@xxxxxxxxxxxxxx
> >
> >  "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@xxxxxxxxxxxxxx

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