Re: [PATCH v7 2/7] sched: move cfs task on a CPU with higher capacity

On Tue, Oct 07, 2014 at 02:13:32PM +0200, Vincent Guittot wrote:

+++ b/kernel/sched/fair.c @@ -5896,6 +5896,18 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group) } /*

• • Check whether the capacity of the rq has been noticeably reduced by side
• • activity. The imbalance_pct is used for the threshold.
• • Return true is the capacity is reduced
• */

+static inline int +check_cpu_capacity(struct rq *rq, struct sched_domain *sd) +{

• return ((rq->cpu_capacity * sd->imbalance_pct) <

• 		(rq->cpu_capacity_orig * 100));
  

+}

+/*

• Group imbalance indicates (and tries to solve) the problem where balancing
• groups is inadequate due to tsk_cpus_allowed() constraints.

@@ -6567,6 +6579,14 @@ static int need_active_balance(struct lb_env *env) */ if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu) return 1;

• /*
  

•  * The src_cpu's capacity is reduced because of other
  

•  * sched_class or IRQs, we trig an active balance to move the
  

•  * task
  

•  */
  

• if (check_cpu_capacity(env->src_rq, sd))
  

• 	return 1;
  

  }

So does it make sense to first check if there's a better candidate at all? By this time we've already iterated the current SD while trying regular load balancing, so we could know this.