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SubjectRe: [PATCH v2 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value
On Thu, Sep 14, 2017 at 10:05:19AM +0900, Byungchul Park wrote:
> 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.

I think, the patch is necessary, isn't it?

> 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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