On 30 September 2014 20:41, Peter Zijlstra peterz@infradead.org wrote:
On Tue, Sep 30, 2014 at 10:41:08AM +0200, Vincent Guittot wrote:
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2a1e6ac..adad532 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6425,13 +6425,14 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
if (env->idle == CPU_IDLE) { /*
* This cpu is idle. If the busiest group load doesn't* have more tasks than the number of available cpu's and* there is no imbalance between this and busiest group* wrt to idle cpu's, it is balanced.
* This cpu is idle. If the busiest group is not overloaded* and there is no imbalance between this and busiest group* wrt to idle cpus, it is balanced. The imbalance becomes* significant if the diff is greater than 1 otherwise we* might end up to just move the imbalance on another group */
if ((local->idle_cpus < busiest->idle_cpus) &&busiest->sum_nr_running <= busiest->group_weight)
if ((local->idle_cpus <= (busiest->idle_cpus + 1)) &&So I'm thick and I don't get this one.. In fact I don't seem to understand the existing code either.
My understand of the original code is that if a group is overloaded (wrt capacity_factor) but has less tasks than CPUs (so overloaded because of rt) and the local group has more idle CPUs then it's worth balancing tasks and load.
I have changed it into : if the busiest group is overloaded or the local has more than 1 idle CPU than the busiest, it makes sense to try to balance tasks in order to balance the avg_load of the groups. But if the local group has only 1 more idle CPU than the busiest, it's probably not possible to leverage the average load load of the groups. We will only move the imbalance from 1 group to another one
If we're idle, and busiest is overloaded, we want to have tasks. Why would we care about number of idle cpus etc..
!(busiest->group_type == group_overloaded))Would not: busiest->group_type != group_overloaded, read more natural? Also, would it make sense to make this the first condition?
that's fair for both remark
goto out_balanced; } else {