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Subject[PATCH v3 03/22] sched: fix find_idlest_group mess logical
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There is 4 situations in the function:
1, no task allowed group;
so min_load = ULONG_MAX, this_load = 0, idlest = NULL
2, only local group task allowed;
so min_load = ULONG_MAX, this_load assigned, idlest = NULL
3, only non-local task group allowed;
so min_load assigned, this_load = 0, idlest != NULL
4, local group + another group are task allowed.
so min_load assigned, this_load assigned, idlest != NULL

Current logical will return NULL in first 3 kinds of scenarios.
And still return NULL, if idlest group is heavier then the
local group in the 4th situation.

Actually, I thought groups in situation 2,3 are also eligible to host
the task. And in 4th situation, agree to bias toward local group.
So, has this patch.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
kernel/sched/fair.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6d3a95d..3c7b09a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3181,6 +3181,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int load_idx)
{
struct sched_group *idlest = NULL, *group = sd->groups;
+ struct sched_group *this_group = NULL;
unsigned long min_load = ULONG_MAX, this_load = 0;
int imbalance = 100 + (sd->imbalance_pct-100)/2;

@@ -3215,14 +3216,19 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,

if (local_group) {
this_load = avg_load;
- } else if (avg_load < min_load) {
+ this_group = group;
+ }
+ if (avg_load < min_load) {
min_load = avg_load;
idlest = group;
}
} while (group = group->next, group != sd->groups);

- if (!idlest || 100*this_load < imbalance*min_load)
- return NULL;
+ if (this_group && idlest != this_group)
+ /* Bias toward our group again */
+ if (100*this_load < imbalance*min_load)
+ idlest = this_group;
+
return idlest;
}

--
1.7.12


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