linux-kernel - Re: [PATCH] drm/scheduler: set current

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Message-ID: <9774ddd6-60d9-245c-77ac-59951c13b263@amd.com>
Date:   Thu, 27 Oct 2022 04:07:26 -0400
From:   Luben Tuikov <luben.tuikov@....com>
To:     brolerliew <brolerliew@...il.com>,
        "Koenig, Christian" <Christian.Koenig@....com>
Cc:     Alex Deucher <alexdeucher@...il.com>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/scheduler: set current_entity to next when remove
 from rq

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@...il.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@...il.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.

Regards,
Luben