The 25% default imbalance threshold for DIE and NUMA domain is large
enough to generate significant unfairness between threads. A typical
example is the case of 11 threads running on 2x4 CPUs. The imbalance of
20% between the 2 groups of 4 cores is just low enough to not trigger
the load balance between the 2 groups. We will have always the same 6
threads on one group of 4 CPUs and the other 5 threads on the other
group of CPUS. With a fair time sharing in each group, we ends up with
+20% running time for the group of 5 threads.
Consider decreasing the imbalance threshold for overloaded case where we
use the load to balance task and to ensure fair time sharing.
Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
---
kernel/sched/topology.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 9079d865a935..1a84b778755d 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1337,7 +1337,7 @@ sd_init(struct sched_domain_topology_level *tl,
.min_interval = sd_weight,
.max_interval = 2*sd_weight,
.busy_factor = 32,
- .imbalance_pct = 125,
+ .imbalance_pct = 117,
.cache_nice_tries = 0,
--
2.17.1
