Re: [RFC PATCH v3 00/16] Core scheduling v3

[Aaron Lu]

On 2019/8/12 23:38, Vineeth Remanan Pillai wrote:
>> I have two other small changes that I think are worth sending out.
>>
>> The first simplify logic in pick_task() and the 2nd avoid task pick all
>> over again when max is preempted. I also refined the previous hack patch to
>> make schedule always happen only for root cfs rq. Please see below for
>> details, thanks.
>>
> I see a potential issue here. With the simplification in pick_task,
> you might introduce a livelock where the match logic spins for ever.
> But you avoid that with the patch 2, by removing the loop if a pick
> preempts max. The potential problem is that, you miss a case where
> the newly picked task might have a match in the sibling on which max
> was selected before. By selecting idle, you ignore the potential match.

Oh that's right, I missed this.

> As of now, the potential match check does not really work because,
> sched_core_find will always return the same task and we do not check
> the whole core_tree for a next match. This is in my TODO list to have
> sched_core_find to return the best next match, if match was preempted.
> But its a bit complex and needs more thought.

Sounds worth to do :-)