[PATCH 5/5] drm/sched: Make use of a "done" list (v2)

Christian König christian.koenig at amd.com
Fri Dec 4 08:16:50 UTC 2020


Am 04.12.20 um 04:17 schrieb Luben Tuikov:
> The drm_sched_job_done() callback now moves done
> jobs from the pending list to a "done" list.
>
> In drm_sched_job_timeout, make use of the status
> returned by a GPU driver job timeout handler to
> decide whether to leave the oldest job in the
> pending list, or to send it off to the done list.
> If a driver's job timeout callback returns a
> status that that job is done, it is added to the
> done list and the done thread woken up. If that
> job needs more time, it is left on the pending
> list and the timeout timer restarted.
>
> The idea is that a GPU driver can check the IP to
> which the passed-in job belongs to and determine
> whether the IP is alive and well, or if it needs
> more time to complete this job and perhaps others
> also executing on it.
>
> In drm_sched_job_timeout(), the main scheduler
> thread is now parked, before calling a driver's
> timeout_job callback, so as to not compete pushing
> jobs down to the GPU while the recovery method is
> taking place.
>
> Eliminate the polling mechanism of picking out done
> jobs from the pending list, i.e. eliminate
> drm_sched_get_cleanup_job().
>
> This also eliminates the eldest job disappearing
> from the pending list, while the driver timeout
> handler is called.
>
> Various other optimizations to the GPU scheduler
> and job recovery are possible with this format.
>
> Signed-off-by: Luben Tuikov <luben.tuikov at amd.com>
>
> Cc: Alexander Deucher <Alexander.Deucher at amd.com>
> Cc: Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Russell King <linux+etnaviv at armlinux.org.uk>
> Cc: Christian Gmeiner <christian.gmeiner at gmail.com>
> Cc: Qiang Yu <yuq825 at gmail.com>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> Cc: Eric Anholt <eric at anholt.net>
>
> v2: Dispell using a done thread, so as to keep
>      the cache hot on the same processor.
> ---
>   drivers/gpu/drm/scheduler/sched_main.c | 247 +++++++++++++------------
>   include/drm/gpu_scheduler.h            |   4 +
>   2 files changed, 134 insertions(+), 117 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index b9876cad94f2..d77180b44998 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -164,7 +164,9 @@ 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.
> + * Move the completed task to the done list,
> + * signal the its fence to mark it finished,
> + * and wake up the worker thread.
>    */
>   static void drm_sched_job_done(struct drm_sched_job *s_job)
>   {
> @@ -176,9 +178,14 @@ static void drm_sched_job_done(struct drm_sched_job *s_job)
>   
>   	trace_drm_sched_process_job(s_fence);
>   
> +	spin_lock(&sched->job_list_lock);
> +	list_move(&s_job->list, &sched->done_list);
> +	spin_unlock(&sched->job_list_lock);
> +

That is racy, as soon as the spinlock is dropped the job and with it the 
s_fence might haven been destroyed.

>   	dma_fence_get(&s_fence->finished);
>   	drm_sched_fence_finished(s_fence);
>   	dma_fence_put(&s_fence->finished);

In other words this here needs to come first.

Regards,
Christian.

> +
>   	wake_up_interruptible(&sched->wake_up_worker);
>   }
>   
> @@ -309,6 +316,37 @@ static void drm_sched_job_begin(struct drm_sched_job *s_job)
>   	spin_unlock(&sched->job_list_lock);
>   }
>   
> +/** drm_sched_job_timeout -- a timer timeout occurred
> + * @work: pointer to work_struct
> + *
> + * First, park the scheduler thread whose IP timed out,
> + * so that we don't race with the scheduler thread pushing
> + * jobs down the IP as we try to investigate what
> + * happened and give drivers a chance to recover.
> + *
> + * Second, take the fist job in the pending list
> + * (oldest), leave it in the pending list and call the
> + * driver's timer timeout callback to find out what
> + * happened, passing this job as the suspect one.
> + *
> + * The driver may return DRM_TASK_STATUS COMPLETE,
> + * which means the task is not in the IP(*) and we move
> + * it to the done list to free it.
> + *
> + * (*) A reason for this would be, say, that the job
> + * completed in due time, or the driver has aborted
> + * this job using driver specific methods in the
> + * timedout_job callback and has now removed it from
> + * the hardware.
> + *
> + * Or, the driver may return DRM_TASK_STATUS_ALIVE, to
> + * indicate that it had inquired about this job, and it
> + * has verified that this job is alive and well, and
> + * that the DRM layer should give this task more time
> + * to complete. In this case, we restart the timeout timer.
> + *
> + * Lastly, we unpark the scheduler thread.
> + */
>   static void drm_sched_job_timedout(struct work_struct *work)
>   {
>   	struct drm_gpu_scheduler *sched;
> @@ -316,37 +354,32 @@ 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 */
> +	kthread_park(sched->thread);
> +
>   	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);
> -
> -		job->sched->ops->timedout_job(job);
> +		int res;
>   
> -		/*
> -		 * 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;
> +		res = job->sched->ops->timedout_job(job);
> +		if (res == DRM_TASK_STATUS_COMPLETE) {
> +			/* 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);
> +			wake_up_interruptible(&sched->wake_up_worker);
> +		} 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);
> +	kthread_unpark(sched->thread);
>   }
>   
>    /**
> @@ -413,24 +446,13 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
>   	kthread_park(sched->thread);
>   
>   	/*
> -	 * Reinsert back the bad job here - now it's safe as
> -	 * drm_sched_get_cleanup_job cannot race against us and release the
> -	 * bad job at this point - we parked (waited for) any in progress
> -	 * (earlier) cleanups and drm_sched_get_cleanup_job will not be called
> -	 * now until the scheduler thread is unparked.
> -	 */
> -	if (bad && bad->sched == sched)
> -		/*
> -		 * Add at the head of the queue to reflect it was the earliest
> -		 * job extracted.
> -		 */
> -		list_add(&bad->list, &sched->pending_list);
> -
> -	/*
> -	 * Iterate the job list from later to  earlier one and either deactive
> -	 * their HW callbacks or remove them from pending list if they already
> -	 * signaled.
> -	 * This iteration is thread safe as sched thread is stopped.
> +	 * Iterate the pending list in reverse order,
> +	 * from most recently submitted to oldest
> +	 * tasks. Tasks which haven't completed, leave
> +	 * them in the pending list, but decrement
> +	 * their hardware run queue count.
> +	 * Else, the fence must've signalled, and the job
> +	 * is in the done list.
>   	 */
>   	list_for_each_entry_safe_reverse(s_job, tmp, &sched->pending_list,
>   					 list) {
> @@ -439,36 +461,52 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
>   					      &s_job->cb)) {
>   			atomic_dec(&sched->hw_rq_count);
>   		} else {
> -			/*
> -			 * remove job from pending_list.
> -			 * Locking here is for concurrent resume timeout
> -			 */
> -			spin_lock(&sched->job_list_lock);
> -			list_del_init(&s_job->list);
> -			spin_unlock(&sched->job_list_lock);
> -
> -			/*
> -			 * Wait for job's HW fence callback to finish using s_job
> -			 * before releasing it.
> -			 *
> -			 * Job is still alive so fence refcount at least 1
> -			 */
> -			dma_fence_wait(&s_job->s_fence->finished, false);
> -
> -			/*
> -			 * We must keep bad job alive for later use during
> -			 * recovery by some of the drivers but leave a hint
> -			 * that the guilty job must be released.
> -			 */
> -			if (bad != s_job)
> -				sched->ops->free_job(s_job);
> -			else
> -				sched->free_guilty = true;
> +			if (bad == s_job) {
> +				/* This is the oldest job on the pending list
> +				 * whose IP timed out. The
> +				 * drm_sched_job_timeout() function calls the
> +				 * driver's timedout_job callback passing @bad,
> +				 * who then calls this function here--as such
> +				 * we shouldn't move @bad or free it. This will
> +				 * be decided by drm_sched_job_timeout() when
> +				 * this function here returns back to the caller
> +				 * (the driver) and the driver's timedout_job
> +				 * callback returns a result to
> +				 * drm_sched_job_timeout().
> +				 */
> +				;
> +			} else {
> +				int res;
> +
> +				/* This job is not the @bad job passed above.
> +				 * Note that perhaps it was *this* job which
> +				 * timed out. The wait below is suspect. Since,
> +				 * it waits with maximum timeout and "intr" set
> +				 * to false, it will either return 0 indicating
> +				 * that the fence has signalled, or negative on
> +				 * error. What if, the whole IP is stuck and
> +				 * this ends up waiting forever?
> +				 *
> +				 * Wait for job's HW fence callback to finish
> +				 * using s_job before releasing it.
> +				 *
> +				 * Job is still alive so fence
> +				 * refcount at least 1
> +				 */
> +				res = dma_fence_wait(&s_job->s_fence->finished,
> +						     false);
> +
> +				if (res == 0)
> +					sched->ops->free_job(s_job);
> +				else
> +					pr_err_once("%s: dma_fence_wait: %d\n",
> +						    sched->name, res);
> +			}
>   		}
>   	}
>   
>   	/*
> -	 * Stop pending timer in flight as we rearm it in  drm_sched_start. This
> +	 * Stop pending timer in flight as we rearm it in drm_sched_start. This
>   	 * avoids the pending timeout work in progress to fire right away after
>   	 * this TDR finished and before the newly restarted jobs had a
>   	 * chance to complete.
> @@ -511,8 +549,9 @@ 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) {
> @@ -665,47 +704,6 @@ 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
> @@ -759,6 +757,25 @@ static bool drm_sched_blocked(struct drm_gpu_scheduler *sched)
>   	return false;
>   }
>   
> +static void drm_sched_free_done(struct drm_gpu_scheduler *sched)
> +{
> +	LIST_HEAD(done_q);
> +
> +	spin_lock(&sched->job_list_lock);
> +	list_splice_init(&sched->done_list, &done_q);
> +	spin_unlock(&sched->job_list_lock);
> +
> +	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);
> +	}
> +}
> +
>   /**
>    * drm_sched_main - main scheduler thread
>    *
> @@ -768,7 +785,7 @@ 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);
> @@ -778,19 +795,14 @@ 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)) ||
> +					 (!list_empty(&sched->done_list)) ||
>   					 (!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);
> -		}
> +		drm_sched_free_done(sched);
>   
>   		if (!entity)
>   			continue;
> @@ -864,6 +876,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>   	init_waitqueue_head(&sched->wake_up_worker);
>   	init_waitqueue_head(&sched->job_scheduled);
>   	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);
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index cedfc5394e52..11278695fed0 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -289,6 +289,7 @@ struct drm_gpu_scheduler {
>   	uint32_t			hw_submission_limit;
>   	long				timeout;
>   	const char			*name;
> +
>   	struct drm_sched_rq		sched_rq[DRM_SCHED_PRIORITY_COUNT];
>   	wait_queue_head_t		wake_up_worker;
>   	wait_queue_head_t		job_scheduled;
> @@ -296,8 +297,11 @@ struct drm_gpu_scheduler {
>   	atomic64_t			job_id_count;
>   	struct delayed_work		work_tdr;
>   	struct task_struct		*thread;
> +
>   	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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