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Date: Thu, 14 Sep 2017 10:05:19 +0900 From: Byungchul Park <byungchul.park@....com> To: peterz@...radead.org, mingo@...nel.org, rostedt@...dmis.org Cc: linux-kernel@...r.kernel.org, juri.lelli@...il.com, kernel-team@....com Subject: [PATCH v2 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value 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@....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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