Re: [Intel-gfx] [PATCH 01/31] drm/i915/gt: Ratelimit heartbeat completion probing

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> The heartbeat runs through a few phases that we expect to complete
> within a certain number of heartbeat intervals. First we must submit the
> heartbeat to the queue, and if the queue is occupied it may take a
> couple of intervals before the heartbeat preempts the workload and is
> submitted to HW. Once running on HW, completion is not instantaneous as
> it may have to first reset the current workload before it itself runs
> through the empty request and signals completion. As such, we know that
> the heartbeat must take at least the preempt reset timeout and before we
> have had a chance to reset the engine, we do not want to issue a global
> reset ourselves (simply so that we only try to do one reset at a time
> and not confuse ourselves by resetting twice and hitting an innocent.)
>
> So by taking into consideration that once running the request must take
> a finite amount of time, we can delay the final completion check to
> accommodate that and avoid checking too early (before we've had a chance
> to handle any engine resets required).
>
> v2: Attach a callback to flush the work immediately upon the heartbeat
> completion and insert the delay before the next.
>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2853
> Suggested-by: CQ Tang <cq.tang@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  .../gpu/drm/i915/gt/intel_engine_heartbeat.c  | 95 ++++++++++++++++---
>  drivers/gpu/drm/i915/gt/intel_engine_types.h  |  1 +
>  .../drm/i915/gt/selftest_engine_heartbeat.c   | 65 ++++++-------
>  drivers/gpu/drm/i915/gt/selftest_execlists.c  |  5 +-
>  4 files changed, 117 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> index 0b062fad1837..209a477af412 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c
> @@ -20,6 +20,18 @@
>   * issue a reset -- in the hope that restores progress.
>   */
>  
> +#define HEARTBEAT_COMPLETION 50u /* milliseconds */
> +
> +static long completion_timeout(const struct intel_engine_cs *engine)
> +{
> +	long timeout = HEARTBEAT_COMPLETION;
> +
> +	if (intel_engine_has_preempt_reset(engine))
> +		timeout += READ_ONCE(engine->props.preempt_timeout_ms);

Was pondering that we dont add slack but the slack is in
the initial value.

> +
> +	return msecs_to_jiffies(timeout);
> +}
> +
>  static bool next_heartbeat(struct intel_engine_cs *engine)
>  {
>  	long delay;
> @@ -29,6 +41,26 @@ static bool next_heartbeat(struct intel_engine_cs *engine)
>  		return false;
>  
>  	delay = msecs_to_jiffies_timeout(delay);
> +
> +	/*
> +	 * Once we submit a heartbeat to the HW, we know that it will take
> +	 * at least a certain amount of time to complete. On a hanging system
> +	 * it will first have to wait for the preempt reset timeout, and
> +	 * then it will take some time for the reset to resume with the
> +	 * heartbeat and for it to complete. So once we have submitted the
> +	 * heartbeat to HW, we can wait a while longer before declaring the
> +	 * engine stuck and forcing a reset ourselves. If we do a reset
> +	 * and the engine is also doing a reset, it is possible that we
> +	 * reset the engine twice, harming an innocent.
> +	 *
> +	 * Before we have sumitted the heartbeat, we do not want to change

s/sumitted/submitted.

> +	 * the interval as we to promote the heartbeat and trigger preemption

s/we to/we want to/ ?
> +	 * in a deterministic time frame.
> +	 */
> +	if (engine->heartbeat.systole &&
> +	    i915_request_is_active(engine->heartbeat.systole))
> +		delay = max(delay, completion_timeout(engine));

I see no harm to just always switch to the max.

> +
>  	if (delay >= HZ)
>  		delay = round_jiffies_up_relative(delay);
>  	mod_delayed_work(system_highpri_wq, &engine->heartbeat.work, delay + 1);
> @@ -48,12 +80,49 @@ heartbeat_create(struct intel_context *ce, gfp_t gfp)
>  	return rq;
>  }
>  
> +static void defibrillator(struct dma_fence *f, struct dma_fence_cb *cb)
> +{
> +	struct intel_engine_cs *engine =
> +		container_of(cb, typeof(*engine), heartbeat.cb);
> +
> +	if (READ_ONCE(engine->heartbeat.systole))

This particular spot is not a problem but we do manipulate
the systole, without lock, in heartbeat().

So I see race in idle_pulse where we swap the systole.

-Mika

> +		mod_delayed_work(system_highpri_wq, &engine->heartbeat.work, 0);
> +}
> +
> +static void
> +untrack_heartbeat(struct intel_engine_cs *engine)
> +{
> +	struct i915_request *rq;
> +
> +	rq = fetch_and_zero(&engine->heartbeat.systole);
> +	if (!rq)
> +		return;
> +
> +	ENGINE_TRACE(engine, "heartbeat " RQ_FMT "completed\n", RQ_ARG(rq));
> +
> +	dma_fence_remove_callback(&rq->fence, &engine->heartbeat.cb);
> +	i915_request_put(rq);
> +}
> +
> +static void
> +track_heartbeat(struct intel_engine_cs *engine, struct i915_request *rq)
> +{
> +	ENGINE_TRACE(engine, "heartbeat " RQ_FMT "started\n", RQ_ARG(rq));
> +
> +	dma_fence_add_callback(&rq->fence,
> +			       &engine->heartbeat.cb,
> +			       defibrillator);
> +	engine->heartbeat.systole = i915_request_get(rq);
> +	if (!next_heartbeat(engine))
> +		untrack_heartbeat(engine);
> +}
> +
>  static void idle_pulse(struct intel_engine_cs *engine, struct i915_request *rq)
>  {
>  	engine->wakeref_serial = READ_ONCE(engine->serial) + 1;
>  	i915_request_add_active_barriers(rq);
>  	if (!engine->heartbeat.systole && intel_engine_has_heartbeat(engine))
> -		engine->heartbeat.systole = i915_request_get(rq);
> +		track_heartbeat(engine, rq);
>  }
>  
>  static void heartbeat_commit(struct i915_request *rq,
> @@ -106,13 +175,8 @@ static void heartbeat(struct work_struct *wrk)
>  	intel_engine_flush_scheduler(engine);
>  
>  	rq = engine->heartbeat.systole;
> -	if (rq && i915_request_completed(rq)) {
> -		ENGINE_TRACE(engine,
> -			     "heartbeat " RQ_FMT "completed\n",
> -			     RQ_ARG(rq));
> -		i915_request_put(rq);
> -		engine->heartbeat.systole = NULL;
> -	}
> +	if (rq && i915_request_completed(rq))
> +		untrack_heartbeat(engine);
>  
>  	if (!intel_engine_pm_get_if_awake(engine))
>  		return;
> @@ -180,6 +244,11 @@ static void heartbeat(struct work_struct *wrk)
>  		goto out;
>  	}
>  
> +	/* Just completed one heartbeat, wait a tick before the next */
> +	if (rq)
> +		goto out;
> +
> +	/* The engine is parking. We can rest until the next user */
>  	serial = READ_ONCE(engine->serial);
>  	if (engine->wakeref_serial == serial)
>  		goto out;
> @@ -198,14 +267,14 @@ static void heartbeat(struct work_struct *wrk)
>  	if (IS_ERR(rq))
>  		goto unlock;
>  
> -	ENGINE_TRACE(engine, "heartbeat " RQ_FMT "started\n", RQ_ARG(rq));
>  	heartbeat_commit(rq, &attr);
>  
>  unlock:
>  	mutex_unlock(&ce->timeline->mutex);
>  out:
> +	intel_engine_flush_scheduler(engine);
>  	if (!engine->i915->params.enable_hangcheck || !next_heartbeat(engine))
> -		i915_request_put(fetch_and_zero(&engine->heartbeat.systole));
> +		untrack_heartbeat(engine);
>  	intel_engine_pm_put(engine);
>  }
>  
> @@ -219,8 +288,10 @@ void intel_engine_unpark_heartbeat(struct intel_engine_cs *engine)
>  
>  void intel_engine_park_heartbeat(struct intel_engine_cs *engine)
>  {
> -	if (cancel_delayed_work(&engine->heartbeat.work))
> -		i915_request_put(fetch_and_zero(&engine->heartbeat.systole));
> +	/* completion may rearm work */
> +	while (cancel_delayed_work(&engine->heartbeat.work))
> +		;
> +	untrack_heartbeat(engine);
>  }
>  
>  void intel_engine_init_heartbeat(struct intel_engine_cs *engine)
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index 7efa6290cc3e..d27a44070cb1 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -322,6 +322,7 @@ struct intel_engine_cs {
>  	struct {
>  		struct delayed_work work;
>  		struct i915_request *systole;
> +		struct dma_fence_cb cb;
>  		unsigned long blocked;
>  	} heartbeat;
>  
> diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> index b2c369317bf1..812c4a168b01 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> @@ -202,47 +202,44 @@ static int cmp_u32(const void *_a, const void *_b)
>  
>  static int __live_heartbeat_fast(struct intel_engine_cs *engine)
>  {
> -	const unsigned int error_threshold = max(20000u, jiffies_to_usecs(6));
> -	struct intel_context *ce;
> -	struct i915_request *rq;
> -	ktime_t t0, t1;
> +	const unsigned int error_threshold =
> +		max(3 * HEARTBEAT_COMPLETION * 1000, jiffies_to_usecs(6));
> +	struct intel_context *ce = engine->kernel_context;
>  	u32 times[5];
>  	int err;
>  	int i;
>  
> -	ce = intel_context_create(engine);
> -	if (IS_ERR(ce))
> -		return PTR_ERR(ce);
> -
>  	intel_engine_pm_get(engine);
>  
>  	err = intel_engine_set_heartbeat(engine, 1);
>  	if (err)
>  		goto err_pm;
>  
> +	flush_delayed_work(&engine->heartbeat.work);
> +	while (engine->heartbeat.systole)
> +		intel_engine_park_heartbeat(engine);
> +
>  	for (i = 0; i < ARRAY_SIZE(times); i++) {
> -		do {
> -			/* Manufacture a tick */
> -			intel_engine_park_heartbeat(engine);
> -			GEM_BUG_ON(engine->heartbeat.systole);
> -			engine->serial++; /*  pretend we are not idle! */
> -			intel_engine_unpark_heartbeat(engine);
> +		struct i915_sched_attr attr = { .priority = I915_PRIORITY_MIN };
> +		struct i915_request *rq;
> +		ktime_t t0, t1;
>  
> -			flush_delayed_work(&engine->heartbeat.work);
> -			if (!delayed_work_pending(&engine->heartbeat.work)) {
> -				pr_err("%s: heartbeat %d did not start\n",
> -				       engine->name, i);
> -				err = -EINVAL;
> -				goto err_pm;
> -			}
> +		GEM_BUG_ON(READ_ONCE(engine->heartbeat.systole));
>  
> -			rcu_read_lock();
> -			rq = READ_ONCE(engine->heartbeat.systole);
> -			if (rq)
> -				rq = i915_request_get_rcu(rq);
> -			rcu_read_unlock();
> -		} while (!rq);
> +		/* Manufacture a tick */
> +		mutex_lock(&ce->timeline->mutex);
> +		rq = heartbeat_create(ce, GFP_KERNEL);
> +		if (!IS_ERR(rq)) {
> +			i915_request_get(rq);
> +			heartbeat_commit(rq, &attr);
> +		}
> +		mutex_unlock(&ce->timeline->mutex);
> +		if (IS_ERR(rq)) {
> +			err = PTR_ERR(rq);
> +			goto err_reset;
> +		}
>  
> +		/* Time how long before the heartbeat monitor checks */
>  		t0 = ktime_get();
>  		while (rq == READ_ONCE(engine->heartbeat.systole))
>  			yield(); /* work is on the local cpu! */
> @@ -275,10 +272,10 @@ static int __live_heartbeat_fast(struct intel_engine_cs *engine)
>  		err = -EINVAL;
>  	}
>  
> +err_reset:
>  	reset_heartbeat(engine);
>  err_pm:
>  	intel_engine_pm_put(engine);
> -	intel_context_put(ce);
>  	return err;
>  }
>  
> @@ -308,20 +305,16 @@ static int __live_heartbeat_off(struct intel_engine_cs *engine)
>  
>  	intel_engine_pm_get(engine);
>  
> +	/* Kick once, so that we change an active heartbeat */
>  	engine->serial++;
> -	flush_delayed_work(&engine->heartbeat.work);
> -	if (!delayed_work_pending(&engine->heartbeat.work)) {
> -		pr_err("%s: heartbeat not running\n",
> -		       engine->name);
> -		err = -EINVAL;
> -		goto err_pm;
> -	}
> +	intel_engine_unpark_heartbeat(engine);
>  
>  	err = intel_engine_set_heartbeat(engine, 0);
>  	if (err)
>  		goto err_pm;
>  
> -	engine->serial++;
> +	/* The next heartbeat work should cancel the heartbeat */
> +	engine->serial++; /* pretend the engine is still active */
>  	flush_delayed_work(&engine->heartbeat.work);
>  	if (delayed_work_pending(&engine->heartbeat.work)) {
>  		pr_err("%s: heartbeat still running\n",
> diff --git a/drivers/gpu/drm/i915/gt/selftest_execlists.c b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> index f625c29023ea..04ded3a2d491 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_execlists.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> @@ -2325,13 +2325,16 @@ static int __cancel_fail(struct live_preempt_cancel *arg)
>  	del_timer_sync(&engine->execlists.preempt);
>  	intel_engine_flush_scheduler(engine);
>  
> +	engine->props.preempt_timeout_ms = 0;
>  	cancel_reset_timeout(engine);
>  
> -	/* after failure, require heartbeats to reset device */
> +	/* after failure, require fast heartbeats to reset device */
>  	intel_engine_set_heartbeat(engine, 1);
>  	err = wait_for_reset(engine, rq, HZ / 2);
>  	intel_engine_set_heartbeat(engine,
>  				   engine->defaults.heartbeat_interval_ms);
> +
> +	engine->props.preempt_timeout_ms = engine->defaults.preempt_timeout_ms;
>  	if (err) {
>  		pr_err("Cancelled inflight0 request did not reset\n");
>  		goto out;
> -- 
> 2.20.1
>
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