When hotplugging cpus out or creating exclusive cpusets (disabling
sched_load_balance) systems which were asymmetric at boot might become
symmetric. In this case leaving the flag set might lead to suboptimal
scheduling decisions.
The arch-code proving the flag doesn't have visibility of the cpuset
configuration so it must either be told by passing a cpumask or the
generic topology code has to verify if the flag should still be set
when taking the actual sched_domain_span() into account. This patch
implements the latter approach.
We need to detect capacity based on calling arch_scale_cpu_capacity()
directly as rq->cpu_capacity_orig hasn't been set yet early in the boot
process.
cc: Ingo Molnar <mi...@redhat.com>
cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmus...@arm.com>
---
kernel/sched/topology.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 71330e0e41db..29c186961345 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1160,6 +1160,26 @@ sd_init(struct sched_domain_topology_level *tl,
sd_id = cpumask_first(sched_domain_span(sd));
/*
+ * Check if cpu_map eclipses cpu capacity asymmetry.
+ */
+
+ if (sd->flags & SD_ASYM_CPUCAPACITY) {
+ int i;
+ bool disable = true;
+ long capacity = arch_scale_cpu_capacity(NULL, sd_id);
+
+ for_each_cpu(i, sched_domain_span(sd)) {
+ if (capacity != arch_scale_cpu_capacity(NULL, i)) {
+ disable = false;
+ break;
+ }
+ }
+
+ if (disable)
+ sd->flags &= ~SD_ASYM_CPUCAPACITY;
+ }
+
+ /*
* Convert topological properties into behaviour.
*/
--
2.7.4
