Re: volanoMark regression with kernel 2.6.26-rc1

Peter Zijlstra
2008-05-14T15:13:23Z

> +#define GROUP_SCALE (2*1024)
> +
> static inline void inc_cpu_load(struct rq *rq, unsigned long load)
> {
> + load *= GROUP_SCALE;
> update_load_add(&rq->load, load);
> }
>
> static inline void dec_cpu_load(struct rq *rq, unsigned long load)
> {
> + load *= GROUP_SCALE;
> update_load_sub(&rq->load, load);
> }

Yeah, this bit makes a huge difference; I do that by:

mkdir /cgroup/foo
for i in `cat /cgroup/tasks`; do echo $i > /cgroup/foo/tasks; done
echo $((1024*1024)) > /cgroup/foo/cpu.shares

I'm still pulling my hairs out on why this makes a difference though - I
eliminated all direct assumption on SCHED_LOAD_SCALE(_FUZZ) with an
average of the weight per task. - but all that doesn't help (much)

A few other things I found that make a significant difference:

+static void update_aggregate(int cpu, struct sched_domain *sd)
+{
+ aggregate_walk_tree(aggregate_get_down, aggregate_get_nop, cpu, sd);
+}

@@ -3224,6 +3189,8 @@ static int move_tasks(struct rq *this_rq, int this_cpu, st
ruct rq *busiest,
unsigned long total_load_moved = 0;
int this_best_prio = this_rq->curr->prio;

+ update_aggregate(this_cpu, sd);
+
do {
total_load_moved +=
class->load_balance(this_rq, this_cpu, busiest,

and

@@ -1169,7 +1168,10 @@ static unsigned long wakeup_gran(struct sched_entity *se)
* More easily preempt - nice tasks, while not making it harder for
* + nice tasks.
*/
- gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
+ if (sched_feat(ASYM_GRAN))
+ gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
+ else
+ gran = calc_delta_fair(sysctl_sched_wakeup_granularity, se);

return gran;
}

the asym logic is wrong wrt shares - it should look at tg->weight