On 11 September 2014 18:15, Peter Zijlstra peterz@infradead.org wrote:
On Tue, Aug 26, 2014 at 01:06:54PM +0200, Vincent Guittot wrote:
+static inline int group_has_free_capacity(struct sg_lb_stats *sgs,
struct lb_env *env){
if ((sgs->group_capacity_orig * 100) >(sgs->group_utilization * env->sd->imbalance_pct))return 1;if (sgs->sum_nr_running < sgs->group_weight)return 1;return 0;+}
+static inline int group_is_overloaded(struct sg_lb_stats *sgs,
struct lb_env *env)+{
if (sgs->sum_nr_running <= sgs->group_weight)return 0;if ((sgs->group_capacity_orig * 100) <(sgs->group_utilization * env->sd->imbalance_pct))return 1;return 0;}
I'm confused about the utilization vs capacity_orig. I see how we should
1st point is that I should compare utilization vs capacity and not capacity_orig. I should have replaced capacity_orig by capacity in the functions above when i move the utilization statistic from rq->avg.runnable_avg_sum to cfs.usage_load_avg. rq->avg.runnable_avg_sum was measuring all activity on the cpu whereas cfs.usage_load_avg integrates only cfs tasks
With this change, we don't need sgs->group_capacity_orig anymore but only sgs->group_capacity. So sgs->group_capacity_orig can be removed as it's no more used in the code as sg_capacity_factor has been removed
maybe scale things with the capacity when comparing between CPUs/groups, but not on the same CPU/group.
I would have expected something simple like:
static inline bool group_has_capacity() { /* Is there a spare cycle? */ if (sgs->group_utilization < sgs->group_weight * SCHED_LOAD_SCALE) return true;
/* Are there less tasks than logical CPUs? */ if (sgs->sum_nr_running < sgs->group_weight) return true; return false;}
Where group_utilization a pure sum of running_avg.
Now this has a hole when there are RT tasks on the system, in that case the utilization will never hit 1, but we could fix that another way. I don't think the capacity_orig thing is right.