Re: [Intel-gfx] [PATCH v3 01/20] drm/sched: entity->rq selection cannot fail

From: "Christian König" <christian.koenig@amd.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
	DRI Development <dri-devel@lists.freedesktop.org>
Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>,
	Jack Zhang <Jack.Zhang1@amd.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Steven Price <steven.price@arm.com>,
	Luben Tuikov <luben.tuikov@amd.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [Intel-gfx] [PATCH v3 01/20] drm/sched: entity->rq selection cannot fail
Date: Fri, 9 Jul 2021 08:53:13 +0200	[thread overview]
Message-ID: <5588d1c3-833b-bd95-69e6-a103f2e8affa@amd.com> (raw)
In-Reply-To: <20210708173754.3877540-2-daniel.vetter@ffwll.ch>

Am 08.07.21 um 19:37 schrieb Daniel Vetter:
> If it does, someone managed to set up a sched_entity without
> schedulers, which is just a driver bug.

NAK, it is perfectly valid for rq selection to fail.

See drm_sched_pick_best():

                 if (!sched->ready) {
                         DRM_WARN("scheduler %s is not ready, skipping",
                                  sched->name);
                         continue;
                 }

This can happen when a device reset fails for some engine.

Regards,
Christian.

>
> We BUG_ON() here because in the next patch drm_sched_job_init() will
> be split up, with drm_sched_job_arm() never failing. And that's the
> part where the rq selection will end up in.
>
> Note that if having an empty sched_list set on an entity is indeed a
> valid use-case, we can keep that check in job_init even after the split
> into job_init/arm.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: Luben Tuikov <luben.tuikov@amd.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
> Cc: Boris Brezillon <boris.brezillon@collabora.com>
> Cc: Jack Zhang <Jack.Zhang1@amd.com>
> ---
>   drivers/gpu/drm/scheduler/sched_entity.c | 2 +-
>   drivers/gpu/drm/scheduler/sched_main.c   | 3 +--
>   2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 79554aa4dbb1..6fc116ee7302 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -45,7 +45,7 @@
>    * @guilty: atomic_t set to 1 when a job on this queue
>    *          is found to be guilty causing a timeout
>    *
> - * Note: the sched_list should have at least one element to schedule
> + * Note: the sched_list must have at least one element to schedule
>    *       the entity
>    *
>    * Returns 0 on success or a negative error code on failure.
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 33c414d55fab..01dd47154181 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -586,8 +586,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
>   	struct drm_gpu_scheduler *sched;
>   
>   	drm_sched_entity_select_rq(entity);
> -	if (!entity->rq)
> -		return -ENOENT;
> +	BUG_ON(!entity->rq);
>   
>   	sched = entity->rq->sched;
>   

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