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sched/fair: Reduce minimal imbalance threshold

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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.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Acked-by: Hillf Danton <hdanton@sina.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-3-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2020-09-21 09:24:22 +02:00 committed by Peter Zijlstra
parent 5a7f555904
commit 2208cdaa56
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/topology.c
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@ -1349,7 +1349,7 @@ sd_init(struct sched_domain_topology_level *tl,
.min_interval = sd_weight, .min_interval = sd_weight,
.max_interval = 2*sd_weight, .max_interval = 2*sd_weight,
.busy_factor = 32, .busy_factor = 32,
.imbalance_pct = 125, .imbalance_pct = 117,
.cache_nice_tries = 0, .cache_nice_tries = 0,