[RFC 10/18] drm/sched: Implement RR via FIFO

[Tvrtko Ursulin]

On 09/01/2025 14:12, Christian König wrote:
> Am 09.01.25 um 14:27 schrieb Tvrtko Ursulin:
>> [SNIP]
>>>> @@ -259,7 +258,7 @@ struct drm_sched_rq {
>>>>       spinlock_t            lock;
>>>>       /* Following members are protected by the @lock: */
>>>> -    struct drm_sched_entity        *current_entity;
>>>> +    ktime_t                rr_deadline;
>>>>       struct list_head        entities;
>>>
>>> If I'm not completely mistaken you can now also nuke this entities 
>>> list if you haven't already removed all users.
>>
>> I had a version which did that too. But then I dropped it in favour of 
>> only keeping entities with queued jobs in the tree. (Before both the 
>> list and the tree contained entities which submitted at least one job 
>> in the past.)
>>
>> I kind of like keeping the tree trimmed (would it lower the rb tree 
>> re-balancing costs?) in which case the full list is needed for that 
>> karma processing business.
> 
> Well, is anybody still using this karma stuff (maybe amdgpu, but we 
> could drop that)? That as well turned out to be a quite broken approach.

Git grep says etnaviv, lima, panfrost, v3d.

> Basically the idea behind karma was that on a crash you re-submit the 
> same job over and over again until it either doesn't crash any more or 
> your karma became to bad.

Well I don't know, TBD I guess. In any case probably best to leave that 
work for a different series to keep this one reasonably focused.

I also still like the idea of keeping the tree pruned of idle entities 
so for me rq->entities list is not a big deal.

> And when you now think of what Einstein once said about insanity then 
> yeah that was also my first thought when I learned about that :)

Right, resubmitting hanging jobs sounds highly questionable indeed.

But it is also the entity->guilty business.

Now if entities were reference counted... ;) The list walk 
hack/workaround in drm_sched_increase_karma could also go away.

Regards,

Tvrtko

>>
>> Regards,
>>
>> Tvrtko
>>
>>>
>>> Regards,
>>> Christian.
>>>
>>>>       struct rb_root_cached rb_tree_root;
>>>>   };
>>>
>