Re: [PATCH] drm/scheduler: set current_entity to next when remove from rq

["Christian König" <christian.koenig@amd.com>]

Am 27.10.22 um 10:07 schrieb Luben Tuikov:
> On 2022-10-27 03:01, Luben Tuikov wrote:
>> On 2022-10-25 13:50, Luben Tuikov wrote:
>>> Looking...
>>>
>>> Regards,
>>> Luben
>>>
>>> On 2022-10-25 09:35, Alex Deucher wrote:
>>>> + Luben
>>>>
>>>> On Tue, Oct 25, 2022 at 2:55 AM brolerliew <brolerliew@gmail.com> wrote:
>>>>> When entity move from one rq to another, current_entity will be set to NULL
>>>>> if it is the moving entity. This make entities close to rq head got
>>>>> selected more frequently, especially when doing load balance between
>>>>> multiple drm_gpu_scheduler.
>>>>>
>>>>> Make current_entity to next when removing from rq.
>>>>>
>>>>> Signed-off-by: brolerliew <brolerliew@gmail.com>
>>>>> ---
>>>>>   drivers/gpu/drm/scheduler/sched_main.c | 5 +++--
>>>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>>>> index 2fab218d7082..00b22cc50f08 100644
>>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>>> @@ -168,10 +168,11 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
>>>>>          spin_lock(&rq->lock);
>>>>>
>>>>>          atomic_dec(rq->sched->score);
>>>>> -       list_del_init(&entity->list);
>>>>>
>>>>>          if (rq->current_entity == entity)
>>>>> -               rq->current_entity = NULL;
>>>>> +               rq->current_entity = list_next_entry(entity, list);
>>>>> +
>>>>> +       list_del_init(&entity->list);
>>>>>
>>>>>          if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
>>>>>                  drm_sched_rq_remove_fifo_locked(entity);
>>>>> --
>>>>> 2.34.1
>>>>>
>> Looks good. I'll pick it up into some other changes I've in tow, and repost
>> along with my changes, as they're somewhat related.
> Actually, the more I look at it, the more I think that we do want to set
> rq->current_entity to NULL in that function, in order to pick the next best entity
> (or scheduler for that matter), the next time around. See sched_entity.c,
> and drm_sched_rq_select_entity() where we start evaluating from the _next_
> entity.
>
> So, it is best to leave it to set it to NULL, for now.

Apart from that this patch here could cause a crash when the entity is 
the last one in the list.

In this case current current_entity would be set to an incorrect upcast 
of the head of the list.

Regards,
Christian.

>
> Regards,
> Luben
>