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Subject[PATCH v2 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value
Date
Currently, migrating tasks to cpu0 unconditionally happens when the
heap is empty, since cp->elements[].cpu was initialized to 0(=cpu0).
We have to distinguish between the empty case and cpu0 to avoid the
unnecessary migrantions. Therefore, it has to return an invalid value
e.i. -1 in that case.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/cpudeadline.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 9f02035..bcf903f 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -138,6 +138,12 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
int best_cpu = cpudl_maximum_cpu(cp);
WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));

+ /*
+ * The heap tree is empry for now, just return.
+ */
+ if (best_cpu == -1)
+ return 0;
+
if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
dl_time_before(dl_se->deadline, cpudl_maximum_dl(cp))) {
if (later_mask)
@@ -265,8 +271,10 @@ int cpudl_init(struct cpudl *cp)
return -ENOMEM;
}

- for_each_possible_cpu(i)
+ for_each_possible_cpu(i) {
+ cp->elements[i].cpu = -1;
cp->elements[i].idx = IDX_INVALID;
+ }

return 0;
}
--
1.9.1
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