On 9 October 2014 13:23, Peter Zijlstra peterz@infradead.org wrote:
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.
i'm not sure to completely catch your point. Normally, f_b_g and f_b_q have already looked at the best candidate when we call need_active_balance. And src_cpu has been elected. Or i have missed your point ?