On 7/8/19 9:41 AM, luca abeni wrote:
> Hi Dietmar,
>
> On Thu, 4 Jul 2019 14:05:22 +0200
> Dietmar Eggemann <dietmar.eggem...@arm.com> wrote:
>
>> On 5/6/19 6:48 AM, Luca Abeni wrote:
>>
>> [...]
>>
>>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>>> index 5b981eeeb944..3436f3d8fa8f 100644
>>> --- a/kernel/sched/deadline.c
>>> +++ b/kernel/sched/deadline.c
>>> @@ -1584,6 +1584,9 @@ select_task_rq_dl(struct task_struct *p, int
>>> cpu, int sd_flag, int flags) if (sd_flag != SD_BALANCE_WAKE)
>>> goto out;
>>>
>>> + if (dl_entity_is_special(&p->dl))
>>> + goto out;
>>
>> I wonder if this is really required. The if condition
>>
>> 1591 if (unlikely(dl_task(curr)) &&
>> 1592 (curr->nr_cpus_allowed < 2 ||
>> 1593 !dl_entity_preempt(&p->dl, &curr->dl)) &&
>> 1594 (p->nr_cpus_allowed > 1)) {
>>
>> further below uses '!dl_entity_preempt(&p->dl, &curr->dl))' which
>> returns 'dl_entity_is_special(a) || ...'
>
> Uhm... I do not remember the details; I remember that the check fixed
> something during the development of the patchset, but I did not check
> if it was still needed when I forward-ported the patches...
>
> So, maybe it worked around some bugs in previous versions of the
> kernel, but is not needed now.
I figured it out in the meantime ... you added a ' ... ||
static_branch_unlikely(&sched_asym_cpucapacity)' in this patch to this
if condition which let's special dl tasks (like sugov:X) enter this
condition e.g. on big.LITTLE.
