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Subject[PATCH 09/11] sched/fair: Split out helper to adjust imbalances between domains
The patch "sched/fair: Allow a small load imbalance between low utilisation
SD_NUMA domains" allows an imbalance when the busiest group has very
few tasks. Move the check to a helper function as it is needed by a later
patch.

No functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/fair.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 24fc90b8036a..b2476ef0b056 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8758,6 +8758,21 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
}
}

+static inline long adjust_numa_imbalance(int imbalance, int src_nr_running)
+{
+ unsigned int imbalance_min;
+
+ /*
+ * Allow a small imbalance based on a simple pair of communicating
+ * tasks that remain local when the source domain is almost idle.
+ */
+ imbalance_min = 2;
+ if (src_nr_running <= imbalance_min)
+ return 0;
+
+ return imbalance;
+}
+
/**
* calculate_imbalance - Calculate the amount of imbalance present within the
* groups of a given sched_domain during load balance.
@@ -8854,18 +8869,9 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
}

/* Consider allowing a small imbalance between NUMA groups */
- if (env->sd->flags & SD_NUMA) {
- unsigned int imbalance_min;
-
- /*
- * Allow a small imbalance based on a simple pair of
- * communicating tasks that remain local when the
- * source domain is almost idle.
- */
- imbalance_min = 2;
- if (busiest->sum_nr_running <= imbalance_min)
- env->imbalance = 0;
- }
+ if (env->sd->flags & SD_NUMA)
+ env->imbalance = adjust_numa_imbalance(env->imbalance,
+ busiest->sum_nr_running);

return;
}
--
2.16.4
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