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Subject[PATCH 2/2] sched: fix a logical error in select_task_rq_fair
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If find_idlest_cpu() return '-1', and sd->child is NULL. The function
select_task_rq_fair will return -1. That is not the function's purpose.

The patch introduced a latest_cpu as temporay varible to store
find_idlest_cpu() return value, and let new_cpu to store the latest
workable cpu. If find_idlest_cpu() doesn't find idlest cpu, we still
have a latest workable cpu.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
kernel/sched/fair.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8a1db69..7e4bab48 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2730,6 +2730,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
int load_idx = sd->forkexec_idx;
struct sched_group *group;
int weight;
+ int latest_cpu;

if (!(sd->flags & sd_flag)) {
sd = sd->child;
@@ -2745,8 +2746,12 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
continue;
}

- new_cpu = find_idlest_cpu(group, p, cpu);
- if (new_cpu == -1 || new_cpu == cpu) {
+ latest_cpu = find_idlest_cpu(group, p, cpu);
+
+ if (latest_cpu != -1)
+ new_cpu = latest_cpu;
+
+ if (latest_cpu == -1 || latest_cpu == cpu) {
/* Now try balancing at a lower domain level of cpu */
sd = sd->child;
continue;
--
1.7.5.4


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