On Sat, Aug 24, 2013 at 03:33:59AM -0700, Paul Turner wrote:
> On Mon, Aug 19, 2013 at 9:01 AM, Peter Zijlstra <pet...@infradead.org> wrote:
> > +++ b/kernel/sched/fair.c
> > @@ -4977,7 +4977,7 @@ static struct rq *find_busiest_queue(str
> > unsigned long busiest_load = 0, busiest_power = SCHED_POWER_SCALE;
> > int i;
> >
> > - for_each_cpu(i, sched_group_cpus(group)) {
> > + for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
> > unsigned long power = power_of(i);
> > unsigned long capacity = DIV_ROUND_CLOSEST(power,
> >
> > SCHED_POWER_SCALE);
> > @@ -4986,9 +4986,6 @@ static struct rq *find_busiest_queue(str
> > if (!capacity)
> > capacity = fix_small_capacity(env->sd, group);
> >
> > - if (!cpumask_test_cpu(i, env->cpus))
> > - continue;
> > -
> > rq = cpu_rq(i);
> > wl = weighted_cpuload(i);
>
> There's no need to actually do the divisions immediately below this also.
>
> e.g.
> unsigned long max_load_power = SCHED_POWER_SCALE;
> ...
> if (wl * max_load_power > max_load * power) {
> max_load = wl;
> max_load_power = power;
> ...
>
> This would actually end up being a little more accurate even.
>
> [ Alternatively without caching max_load_power we could compare wl *
> power vs max_load * SCHED_POWER_SCALE. ]
You've got me confused again. You're talking about something like the
below?
I suppose the problem with that is that we could keep selecting the
busiest rq with an unmovable task due to:
move_tasks():
if ((load / 2) > env->imbalance)
goto next;
That said, the condition in fbq() should at least be modified to match
this. Now the entire capacity crap comes from:
bdb94aa sched: Try to deal with low capacity
But thinking a little more about it, if power drops that low imbalance
is likely to be _huge_ and we'd not meet that condition. Now if only I
wrote a more comprehensive Changelog and explained why that wouldn't be
the case. /me kicks himself.
---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4990,28 +4990,12 @@ static struct sched_group *find_busiest_
static struct rq *find_busiest_queue(struct lb_env *env,
struct sched_group *group)
{
- struct rq *busiest = NULL, *rq;
unsigned long busiest_load = 0, busiest_power = 1;
+ struct rq *busiest = NULL;
int i;
for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
- unsigned long power = power_of(i);
- unsigned long capacity = DIV_ROUND_CLOSEST(power,
- SCHED_POWER_SCALE);
- unsigned long wl;
-
- if (!capacity)
- capacity = fix_small_capacity(env->sd, group);
-
- rq = cpu_rq(i);
- wl = weighted_cpuload(i);
-
- /*
- * When comparing with imbalance, use weighted_cpuload()
- * which is not scaled with the cpu power.
- */
- if (capacity && rq->nr_running == 1 && wl > env->imbalance)
- continue;
+ unsigned long wl = weighted_cpuload(i);
/*
* For the load comparisons with the other cpu's, consider
@@ -5027,7 +5011,7 @@ static struct rq *find_busiest_queue(str
if (wl * busiest_power > busiest_load * power) {
busiest_load = wl;
busiest_power = power;
- busiest = rq;
+ busiest = cpu_rq(i);
}
}
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