Re: [PATCH 6/6] drm/sched: Make use of a "done" thread

[Luben Tuikov <luben.tuikov@amd.com>]

On 2020-11-25 06:09, Steven Price wrote:
> On 25/11/2020 03:17, Luben Tuikov wrote:
>> Add a "done" list to which all completed jobs are added
>> to be freed. The drm_sched_job_done() callback is the
>> producer of jobs to this list.
>>
>> Add a "done" thread which consumes from the done list
>> and frees up jobs. Now, the main scheduler thread only
>> pushes jobs to the GPU and the "done" thread frees them
>> up, on the way out of the GPU when they've completed
>> execution.
> 
> Generally I'd be in favour of a "done thread" as I think there are some 
> murky corners of Panfrost's locking that would be helped by deferring 
> the free_job() callback.

Check my response to his email.

It seems you're okay with a separate thread, when both threads
could be working concurrently, and Christian wants
a single thread doing all this. You should probably address
this in a follow-up to his email, so this can be hashed out.

> 
> But I think you're trying to do too much in one patch here. And as 
> Christian has pointed out there's some dodgy looking changes to locking 
> which aren't explained.

I've addressed this in my response to his email, check it out.

So, if you're in favour of a separate thread working concurrently,
please follow up to his email, so this can be hashed out.

Thanks and Regards,
Luben

> 
> Steve
> 
>>
>> Make use of the status returned by the GPU driver
>> timeout handler to decide whether to leave the job in
>> the pending list, or to send it off to the done list.
>> If a job is done, it is added to the done list and the
>> done thread woken up. If a job needs more time, it is
>> left on the pending list and the timeout timer
>> restarted.
>>
>> Eliminate the polling mechanism of picking out done
>> jobs from the pending list, i.e. eliminate
>> drm_sched_get_cleanup_job(). Now the main scheduler
>> thread only pushes jobs down to the GPU.
>>
>> Various other optimizations to the GPU scheduler
>> and job recovery are possible with this format.
>>
>> Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
>> ---
>>   drivers/gpu/drm/scheduler/sched_main.c | 173 +++++++++++++------------
>>   include/drm/gpu_scheduler.h            |  14 ++
>>   2 files changed, 101 insertions(+), 86 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>> index 3eb7618a627d..289ae68cd97f 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -164,7 +164,8 @@ drm_sched_rq_select_entity(struct drm_sched_rq *rq)
>>    * drm_sched_job_done - complete a job
>>    * @s_job: pointer to the job which is done
>>    *
>> - * Finish the job's fence and wake up the worker thread.
>> + * Finish the job's fence, move it to the done list,
>> + * and wake up the done thread.
>>    */
>>   static void drm_sched_job_done(struct drm_sched_job *s_job)
>>   {
>> @@ -179,7 +180,12 @@ static void drm_sched_job_done(struct drm_sched_job *s_job)
>>   	dma_fence_get(&s_fence->finished);
>>   	drm_sched_fence_finished(s_fence);
>>   	dma_fence_put(&s_fence->finished);
>> -	wake_up_interruptible(&sched->wake_up_worker);
>> +
>> +	spin_lock(&sched->job_list_lock);
>> +	list_move(&s_job->list, &sched->done_list);
>> +	spin_unlock(&sched->job_list_lock);
>> +
>> +	wake_up_interruptible(&sched->done_wait_q);
>>   }
>>   
>>   /**
>> @@ -221,11 +227,10 @@ bool drm_sched_dependency_optimized(struct dma_fence* fence,
>>   EXPORT_SYMBOL(drm_sched_dependency_optimized);
>>   
>>   /**
>> - * drm_sched_start_timeout - start timeout for reset worker
>> - *
>> - * @sched: scheduler instance to start the worker for
>> + * drm_sched_start_timeout - start a timeout timer
>> + * @sched: scheduler instance whose job we're timing
>>    *
>> - * Start the timeout for the given scheduler.
>> + * Start a timeout timer for the given scheduler.
>>    */
>>   static void drm_sched_start_timeout(struct drm_gpu_scheduler *sched)
>>   {
>> @@ -305,8 +310,8 @@ static void drm_sched_job_begin(struct drm_sched_job *s_job)
>>   
>>   	spin_lock(&sched->job_list_lock);
>>   	list_add_tail(&s_job->list, &sched->pending_list);
>> -	drm_sched_start_timeout(sched);
>>   	spin_unlock(&sched->job_list_lock);
>> +	drm_sched_start_timeout(sched);
>>   }
>>   
>>   static void drm_sched_job_timedout(struct work_struct *work)
>> @@ -316,37 +321,30 @@ static void drm_sched_job_timedout(struct work_struct *work)
>>   
>>   	sched = container_of(work, struct drm_gpu_scheduler, work_tdr.work);
>>   
>> -	/* Protects against concurrent deletion in drm_sched_get_cleanup_job */
>>   	spin_lock(&sched->job_list_lock);
>>   	job = list_first_entry_or_null(&sched->pending_list,
>>   				       struct drm_sched_job, list);
>> +	spin_unlock(&sched->job_list_lock);
>>   
>>   	if (job) {
>> -		/*
>> -		 * Remove the bad job so it cannot be freed by concurrent
>> -		 * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
>> -		 * is parked at which point it's safe.
>> -		 */
>> -		list_del_init(&job->list);
>> -		spin_unlock(&sched->job_list_lock);
>> +		int res;
>>   
>> -		job->sched->ops->timedout_job(job);
>> +		job->job_status |= DRM_JOB_STATUS_TIMEOUT;
>> +		res = job->sched->ops->timedout_job(job);
>> +		if (res == 0) {
>> +			/* The job is out of the device.
>> +			 */
>> +			spin_lock(&sched->job_list_lock);
>> +			list_move(&job->list, &sched->done_list);
>> +			spin_unlock(&sched->job_list_lock);
>>   
>> -		/*
>> -		 * Guilty job did complete and hence needs to be manually removed
>> -		 * See drm_sched_stop doc.
>> -		 */
>> -		if (sched->free_guilty) {
>> -			job->sched->ops->free_job(job);
>> -			sched->free_guilty = false;
>> +			wake_up_interruptible(&sched->done_wait_q);
>> +		} else {
>> +			/* The job needs more time.
>> +			 */
>> +			drm_sched_start_timeout(sched);
>>   		}
>> -	} else {
>> -		spin_unlock(&sched->job_list_lock);
>>   	}
>> -
>> -	spin_lock(&sched->job_list_lock);
>> -	drm_sched_start_timeout(sched);
>> -	spin_unlock(&sched->job_list_lock);
>>   }
>>   
>>    /**
>> @@ -511,15 +509,13 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
>>   			else if (r)
>>   				DRM_ERROR("fence add callback failed (%d)\n",
>>   					  r);
>> -		} else
>> +		} else {
>>   			drm_sched_job_done(s_job);
>> +		}
>>   	}
>>   
>> -	if (full_recovery) {
>> -		spin_lock(&sched->job_list_lock);
>> +	if (full_recovery)
>>   		drm_sched_start_timeout(sched);
>> -		spin_unlock(&sched->job_list_lock);
>> -	}
>>   
>>   	kthread_unpark(sched->thread);
>>   }
>> @@ -667,47 +663,6 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched)
>>   	return entity;
>>   }
>>   
>> -/**
>> - * drm_sched_get_cleanup_job - fetch the next finished job to be destroyed
>> - *
>> - * @sched: scheduler instance
>> - *
>> - * Returns the next finished job from the pending list (if there is one)
>> - * ready for it to be destroyed.
>> - */
>> -static struct drm_sched_job *
>> -drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
>> -{
>> -	struct drm_sched_job *job;
>> -
>> -	/*
>> -	 * Don't destroy jobs while the timeout worker is running  OR thread
>> -	 * is being parked and hence assumed to not touch pending_list
>> -	 */
>> -	if ((sched->timeout != MAX_SCHEDULE_TIMEOUT &&
>> -	    !cancel_delayed_work(&sched->work_tdr)) ||
>> -	    kthread_should_park())
>> -		return NULL;
>> -
>> -	spin_lock(&sched->job_list_lock);
>> -
>> -	job = list_first_entry_or_null(&sched->pending_list,
>> -				       struct drm_sched_job, list);
>> -
>> -	if (job && dma_fence_is_signaled(&job->s_fence->finished)) {
>> -		/* remove job from pending_list */
>> -		list_del_init(&job->list);
>> -	} else {
>> -		job = NULL;
>> -		/* queue timeout for next job */
>> -		drm_sched_start_timeout(sched);
>> -	}
>> -
>> -	spin_unlock(&sched->job_list_lock);
>> -
>> -	return job;
>> -}
>> -
>>   /**
>>    * drm_sched_pick_best - Get a drm sched from a sched_list with the least load
>>    * @sched_list: list of drm_gpu_schedulers
>> @@ -761,6 +716,44 @@ static bool drm_sched_blocked(struct drm_gpu_scheduler *sched)
>>   	return false;
>>   }
>>   
>> +/**
>> + * drm_sched_done - free done tasks
>> + * @param: pointer to a scheduler instance
>> + *
>> + * Returns 0.
>> + */
>> +static int drm_sched_done(void *param)
>> +{
>> +	struct drm_gpu_scheduler *sched = param;
>> +
>> +	do {
>> +		LIST_HEAD(done_q);
>> +
>> +		wait_event_interruptible(sched->done_wait_q,
>> +					 kthread_should_stop() ||
>> +					 !list_empty(&sched->done_list));
>> +
>> +		spin_lock(&sched->job_list_lock);
>> +		list_splice_init(&sched->done_list, &done_q);
>> +		spin_unlock(&sched->job_list_lock);
>> +
>> +		if (list_empty(&done_q))
>> +			continue;
>> +
>> +		while (!list_empty(&done_q)) {
>> +			struct drm_sched_job *job;
>> +
>> +			job = list_first_entry(&done_q,
>> +					       struct drm_sched_job,
>> +					       list);
>> +			list_del_init(&job->list);
>> +			sched->ops->free_job(job);
>> +		}
>> +	} while (!kthread_should_stop());
>> +
>> +	return 0;
>> +}
>> +
>>   /**
>>    * drm_sched_main - main scheduler thread
>>    *
>> @@ -770,7 +763,7 @@ static bool drm_sched_blocked(struct drm_gpu_scheduler *sched)
>>    */
>>   static int drm_sched_main(void *param)
>>   {
>> -	struct drm_gpu_scheduler *sched = (struct drm_gpu_scheduler *)param;
>> +	struct drm_gpu_scheduler *sched = param;
>>   	int r;
>>   
>>   	sched_set_fifo_low(current);
>> @@ -780,20 +773,12 @@ static int drm_sched_main(void *param)
>>   		struct drm_sched_fence *s_fence;
>>   		struct drm_sched_job *sched_job;
>>   		struct dma_fence *fence;
>> -		struct drm_sched_job *cleanup_job = NULL;
>>   
>>   		wait_event_interruptible(sched->wake_up_worker,
>> -					 (cleanup_job = drm_sched_get_cleanup_job(sched)) ||
>>   					 (!drm_sched_blocked(sched) &&
>>   					  (entity = drm_sched_select_entity(sched))) ||
>>   					 kthread_should_stop());
>>   
>> -		if (cleanup_job) {
>> -			sched->ops->free_job(cleanup_job);
>> -			/* queue timeout for next job */
>> -			drm_sched_start_timeout(sched);
>> -		}
>> -
>>   		if (!entity)
>>   			continue;
>>   
>> @@ -820,8 +805,7 @@ static int drm_sched_main(void *param)
>>   			if (r == -ENOENT)
>>   				drm_sched_job_done(sched_job);
>>   			else if (r)
>> -				DRM_ERROR("fence add callback failed (%d)\n",
>> -					  r);
>> +				DRM_ERROR("fence add callback failed (%d)\n", r);
>>   			dma_fence_put(fence);
>>   		} else {
>>   			if (IS_ERR(fence))
>> @@ -865,7 +849,9 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   
>>   	init_waitqueue_head(&sched->wake_up_worker);
>>   	init_waitqueue_head(&sched->job_scheduled);
>> +	init_waitqueue_head(&sched->done_wait_q);
>>   	INIT_LIST_HEAD(&sched->pending_list);
>> +	INIT_LIST_HEAD(&sched->done_list);
>>   	spin_lock_init(&sched->job_list_lock);
>>   	atomic_set(&sched->hw_rq_count, 0);
>>   	INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
>> @@ -881,6 +867,21 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   		return ret;
>>   	}
>>   
>> +	snprintf(sched->thread_done_name, DRM_THREAD_NAME_LEN, "%s%s",
>> +		 sched->name, "-done");
>> +	sched->thread_done_name[DRM_THREAD_NAME_LEN - 1] = '\0';
>> +	sched->thread_done = kthread_run(drm_sched_done, sched,
>> +					 sched->thread_done_name);
>> +	if (IS_ERR(sched->thread_done)) {
>> +		ret = kthread_stop(sched->thread);
>> +		if (!ret) {
>> +			/* free_kthread_struct(sched->thread); */
>> +			sched->thread = NULL;
>> +		}
>> +		DRM_ERROR("Failed to start thread %s", sched->thread_done_name);
>> +		return ret;
>> +	}
>> +
>>   	sched->ready = true;
>>   	return 0;
>>   }
>> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
>> index 3a5686c3b5e9..b282d6158b50 100644
>> --- a/include/drm/gpu_scheduler.h
>> +++ b/include/drm/gpu_scheduler.h
>> @@ -169,6 +169,12 @@ struct drm_sched_fence {
>>   
>>   struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
>>   
>> +enum drm_job_status {
>> +	DRM_JOB_STATUS_NONE    = 0 << 0,
>> +	DRM_JOB_STATUS_DONE    = 1 << 0,
>> +	DRM_JOB_STATUS_TIMEOUT = 1 << 1,
>> +};
>> +
>>   /**
>>    * struct drm_sched_job - A job to be run by an entity.
>>    *
>> @@ -198,6 +204,7 @@ struct drm_sched_job {
>>   	uint64_t			id;
>>   	atomic_t			karma;
>>   	enum drm_sched_priority		s_priority;
>> +	enum drm_job_status             job_status;
>>   	struct drm_sched_entity         *entity;
>>   	struct dma_fence_cb		cb;
>>   };
>> @@ -284,15 +291,22 @@ struct drm_gpu_scheduler {
>>   	uint32_t			hw_submission_limit;
>>   	long				timeout;
>>   	const char			*name;
>> +	char                            thread_done_name[DRM_THREAD_NAME_LEN];
>> +
>>   	struct drm_sched_rq		sched_rq[DRM_SCHED_PRIORITY_COUNT];
>>   	wait_queue_head_t		wake_up_worker;
>>   	wait_queue_head_t		job_scheduled;
>> +	wait_queue_head_t               done_wait_q;
>>   	atomic_t			hw_rq_count;
>>   	atomic64_t			job_id_count;
>>   	struct delayed_work		work_tdr;
>>   	struct task_struct		*thread;
>> +	struct task_struct		*thread_done;
>> +
>>   	struct list_head		pending_list;
>> +	struct list_head                done_list;
>>   	spinlock_t			job_list_lock;
>> +
>>   	int				hang_limit;
>>   	atomic_t                        score;
>>   	bool				ready;
>>
> 

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