Hey Dietmar,
On 5/22/2017 3:48 AM, Dietmar Eggemann wrote:
On 19/05/17 14:31, Dietmar Eggemann wrote:
On 18/05/17 20:36, Jeffrey Hugo wrote:
[...]
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d711093..a5d41b1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8220,7 +8220,24 @@ static int load_balance(int this_cpu, struct rq *this_rq,
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(env.flags & LBF_ALL_PINNED)) {
cpumask_clear_cpu(cpu_of(busiest), cpus);
- if (!cpumask_empty(cpus)) {
+ /*
+ * dst_cpu is not a valid busiest cpu in the following
+ * check since load cannot be pulled from dst_cpu to be
+ * put on dst_cpu.
+ */
+ cpumask_clear_cpu(env.dst_cpu, cpus);
+ /*
+ * Go back to "redo" iff the load-balance cpumask
+ * contains other potential busiest cpus for the
+ * current sched domain.
+ */
+ if (cpumask_intersects(cpus,
sched_domain_span(env.sd))) {
+ /*
+ * Now that the check has passed, reenable
+ * dst_cpu so that load can be calculated on
+ * it in the redo path.
+ */
+ cpumask_set_cpu(env.dst_cpu, cpus);
IMHO, this will work nicely and its way easier.
This was too quick ... if we still have other potential dst cpus
available and cpu_of(busiest) is the latest src cpu then this will fail.
It does work on sd with 'group_weight == 1', e.g. your MC sd 'sd->child
== NULL'.
But IMHO 'group_imbalance' propagation has to work on higher sd levels
as well.
Can you clarify the fail case you are seeing? We are only aware of
dst_cpu being changed under [1] where a dst_cpu will try to move work to
one of its sched_group siblings.
I'm also not entirely sure I understand what you mean about the flag
being propagated to higher sd levels.
Another idea might be to check if the LBF_ALL_PINNED is set when we
check if we should clean the imbalance flag.
@@ -8307,14 +8307,13 @@ static int load_balance(int this_cpu, struct rq
*this_rq,
* We reach balance although we may have faced some affinity
* constraints. Clear the imbalance flag if it was set.
*/
- if (sd_parent) {
+ if (sd_parent && !(env.flags & LBF_ALL_PINNED)) {
int *group_imbalance = &sd_parent->groups->sgc->imbalance;
if (*group_imbalance)
*group_imbalance = 0;
}
[...]
[1] -
http://elixir.free-electrons.com/linux/latest/source/kernel/sched/fair.c#L8140
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