Re: [PATCH 1/2] drm/i915: Fix __wait_seqno to use true infinite timeouts

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On Mon, Aug 26, 2013 at 02:51:53PM +0100, Chris Wilson wrote:
> When we switched to always using a timeout in conjunction with
> wait_seqno, we lost the ability to detect missed interrupts. Since, we
> have had issues with interrupts on a number of generations, and they are
> required to be delivered in a timely fashion for a smooth UX, it is
> important that we do log errors found in the wild and prevent the
> display stalling for upwards of 1s every time the seqno interrupt is
> missed.
> 
> Rather than continue to fix up the timeouts to work around the interface
> impedence in wait_event_*(), open code the combination of
> wait_event[_interruptible][_timeout], and use the exposed timer to
> poll for seqno should we detect a lost interrupt.
> 
> v2: In order to satisfy the debug requirement of logging missed
> interrupts with the real world requirments of making machines work even
> if interrupts are hosed, we revert to polling after detecting a missed
> interrupt.
> 
> v3: Throw in a debugfs interface to simulate broken hw not reporting
> interrupts.

This interface should be a separate patch.

> 
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c   |  68 ++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_drv.h       |   5 ++
>  drivers/gpu/drm/i915/i915_gem.c       | 114 ++++++++++++++++++++--------------
>  drivers/gpu/drm/i915/i915_gpu_error.c |   1 +
>  drivers/gpu/drm/i915/i915_irq.c       |  11 ++--
>  5 files changed, 148 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 55ab924..e823169 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1876,6 +1876,72 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_ring_stop_fops,
>  			i915_ring_stop_get, i915_ring_stop_set,
>  			"0x%08llx\n");
>  
> +static int
> +i915_ring_missed_irq_get(void *data, u64 *val)
> +{
> +	struct drm_device *dev = data;
> +	drm_i915_private_t *dev_priv = dev->dev_private;
> +
> +	*val = dev_priv->gpu_error.missed_irq_rings;
> +	return 0;
> +}
> +
> +static int
> +i915_ring_missed_irq_set(void *data, u64 val)
> +{
> +	struct drm_device *dev = data;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	int ret;
> +
> +	/* Lock against concurrent debugfs callers */
> +	ret = mutex_lock_interruptible(&dev->struct_mutex);
> +	if (ret)
> +		return ret;
> +	dev_priv->gpu_error.missed_irq_rings = val;
> +	mutex_unlock(&dev->struct_mutex);
> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(i915_ring_missed_irq_fops,
> +			i915_ring_missed_irq_get, i915_ring_missed_irq_set,
> +			"0x%08llx\n");
> +
> +static int
> +i915_ring_test_irq_get(void *data, u64 *val)
> +{
> +	struct drm_device *dev = data;
> +	drm_i915_private_t *dev_priv = dev->dev_private;
> +
> +	*val = dev_priv->gpu_error.test_irq_rings;
> +
> +	return 0;
> +}
> +
> +static int
> +i915_ring_test_irq_set(void *data, u64 val)
> +{
> +	struct drm_device *dev = data;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	int ret;
> +
> +	DRM_DEBUG_DRIVER("Masking interrupts on rings 0x%08llx\n", val);
> +
> +	/* Lock against concurrent debugfs callers */
> +	ret = mutex_lock_interruptible(&dev->struct_mutex);
> +	if (ret)
> +		return ret;
> +
> +	dev_priv->gpu_error.test_irq_rings = val;
> +	mutex_unlock(&dev->struct_mutex);
> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(i915_ring_test_irq_fops,
> +			i915_ring_test_irq_get, i915_ring_test_irq_set,
> +			"0x%08llx\n");
> +
>  #define DROP_UNBOUND 0x1
>  #define DROP_BOUND 0x2
>  #define DROP_RETIRE 0x4
> @@ -2269,6 +2335,8 @@ static struct i915_debugfs_files {
>  	{"i915_min_freq", &i915_min_freq_fops},
>  	{"i915_cache_sharing", &i915_cache_sharing_fops},
>  	{"i915_ring_stop", &i915_ring_stop_fops},
> +	{"i915_ring_missed_irq", &i915_ring_missed_irq_fops},
> +	{"i915_ring_test_irq", &i915_ring_test_irq_fops},
>  	{"i915_gem_drop_caches", &i915_drop_caches_fops},
>  	{"i915_error_state", &i915_error_state_fops},
>  	{"i915_next_seqno", &i915_next_seqno_fops},
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 84b95b1..ac6db6e 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -993,6 +993,8 @@ struct i915_gpu_error {
>  
>  	unsigned long last_reset;
>  
> +	unsigned long missed_irq_rings;
> +
>  	/**
>  	 * State variable and reset counter controlling the reset flow
>  	 *
> @@ -1031,6 +1033,9 @@ struct i915_gpu_error {
>  
>  	/* For gpu hang simulation. */
>  	unsigned int stop_rings;
> +
> +	/* For missed irq/seqno simulation. */
> +	unsigned int test_irq_rings;
>  };
>  
>  enum modeset_restore {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index ccfebf5..4ed782f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -970,6 +970,17 @@ i915_gem_check_olr(struct intel_ring_buffer *ring, u32 seqno)
>  	return ret;
>  }
>  
> +static void fake_irq(unsigned long data)
> +{
> +	wake_up_process((struct task_struct *)data);
> +}
> +
> +static bool missed_irq(struct drm_i915_private *dev_priv,
> +		       struct intel_ring_buffer *ring)
> +{
> +	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
> +}
> +
>  /**
>   * __wait_seqno - wait until execution of seqno has finished
>   * @ring: the ring expected to report seqno
> @@ -993,10 +1004,9 @@ static int __wait_seqno(struct intel_ring_buffer *ring, u32 seqno,
>  			bool interruptible, struct timespec *timeout)
>  {
>  	drm_i915_private_t *dev_priv = ring->dev->dev_private;
> -	struct timespec before, now, wait_time={1,0};
> -	unsigned long timeout_jiffies;
> -	long end;
> -	bool wait_forever = true;
> +	struct timespec before, now;
> +	DEFINE_WAIT(wait);
> +	long timeout_jiffies;
>  	int ret;
>  
>  	WARN(dev_priv->pc8.irqs_disabled, "IRQs disabled\n");
> @@ -1004,51 +1014,71 @@ static int __wait_seqno(struct intel_ring_buffer *ring, u32 seqno,
>  	if (i915_seqno_passed(ring->get_seqno(ring, true), seqno))
>  		return 0;
>  
> -	trace_i915_gem_request_wait_begin(ring, seqno);
> -
> -	if (timeout != NULL) {
> -		wait_time = *timeout;
> -		wait_forever = false;
> -	}
> -
> -	timeout_jiffies = timespec_to_jiffies_timeout(&wait_time);
> +	timeout_jiffies = timeout ? timespec_to_jiffies_timeout(timeout) : 1;
>  
> -	if (WARN_ON(!ring->irq_get(ring)))
> +	if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)) &&
> +	    WARN_ON(!ring->irq_get(ring)))
>  		return -ENODEV;
>  
> -	/* Record current time in case interrupted by signal, or wedged * */
> +	/* Record current time in case interrupted by signal, or wedged */
> +	trace_i915_gem_request_wait_begin(ring, seqno);
>  	getrawmonotonic(&before);
> +	for (;;) {
> +		struct timer_list timer;
> +		unsigned long expire;
>  
> -#define EXIT_COND \
> -	(i915_seqno_passed(ring->get_seqno(ring, false), seqno) || \
> -	 i915_reset_in_progress(&dev_priv->gpu_error) || \
> -	 reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> -	do {
> -		if (interruptible)
> -			end = wait_event_interruptible_timeout(ring->irq_queue,
> -							       EXIT_COND,
> -							       timeout_jiffies);
> -		else
> -			end = wait_event_timeout(ring->irq_queue, EXIT_COND,
> -						 timeout_jiffies);
> +		prepare_to_wait(&ring->irq_queue, &wait,
> +				interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
>  
>  		/* We need to check whether any gpu reset happened in between
>  		 * the caller grabbing the seqno and now ... */
> -		if (reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> -			end = -EAGAIN;
> +		if (reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter)) {
> +			/* ... but upgrade the -EGAIN to an -EIO if the gpu
                                                ^ EAGAIN (I realize it's
                                                copypasta)
> +			 * is truely gone. */
                                ^ truly
> +			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> +			if (ret == 0)
> +				ret = -EAGAIN;
> +			break;
> +		}
>  
> -		/* ... but upgrade the -EGAIN to an -EIO if the gpu is truely
> -		 * gone. */
> -		ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> -		if (ret)
> -			end = ret;
> -	} while (end == 0 && wait_forever);
> +		if (i915_seqno_passed(ring->get_seqno(ring, false), seqno)) {
> +			ret = 0;
> +			break;
> +		}
> +
> +		if (interruptible && signal_pending(current)) {
> +			ret = -ERESTARTSYS;
> +			break;
> +		}
> +

Not sure, but I think the signal check should come first.  As long as
you've thought about it, I'm okay with whatever.

> +		if (timeout_jiffies <= 0) {
> +			ret = -ETIME;
> +			break;
> +		}
>  
> +		timer.function = NULL;
> +		if (timeout || missed_irq(dev_priv, ring)) {
> +			setup_timer_on_stack(&timer, fake_irq, (unsigned long)current);
> +			expire = jiffies + (missed_irq(dev_priv, ring) ? 1: timeout_jiffies);
> +			mod_timer(&timer, expire);
> +		}

Isn't this just a fancy schedule_timeout_interruptible?

> +
> +		schedule();
> +
> +		if (timeout)
> +			timeout_jiffies = expire - jiffies;
> +
> +		if (timer.function) {
> +			del_singleshot_timer_sync(&timer);
> +			destroy_timer_on_stack(&timer);
> +		}
> +	}
>  	getrawmonotonic(&now);
> +	trace_i915_gem_request_wait_end(ring, seqno);
>  
>  	ring->irq_put(ring);
> -	trace_i915_gem_request_wait_end(ring, seqno);
> -#undef EXIT_COND
> +
> +	finish_wait(&ring->irq_queue, &wait);
>  
>  	if (timeout) {
>  		struct timespec sleep_time = timespec_sub(now, before);
> @@ -1057,17 +1087,7 @@ static int __wait_seqno(struct intel_ring_buffer *ring, u32 seqno,
>  			set_normalized_timespec(timeout, 0, 0);
>  	}
>  
> -	switch (end) {
> -	case -EIO:
> -	case -EAGAIN: /* Wedged */
> -	case -ERESTARTSYS: /* Signal */
> -		return (int)end;
> -	case 0: /* Timeout */
> -		return -ETIME;
> -	default: /* Completed */
> -		WARN_ON(end < 0); /* We're not aware of other errors */
> -		return 0;
> -	}
> +	return ret;
>  }
>  
>  /**
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 558e568..62368f4 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -288,6 +288,7 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
>  	err_printf(m, "FORCEWAKE: 0x%08x\n", error->forcewake);
>  	err_printf(m, "DERRMR: 0x%08x\n", error->derrmr);
>  	err_printf(m, "CCID: 0x%08x\n", error->ccid);
> +	err_printf(m, "Missed interrupts: 0x%08lx\n", dev_priv->gpu_error.missed_irq_rings);
>  
>  	for (i = 0; i < dev_priv->num_fence_regs; i++)
>  		err_printf(m, "  fence[%d] = %08llx\n", i, error->fence[i]);
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index a03b445..7ebf105 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1972,10 +1972,13 @@ static void i915_hangcheck_elapsed(unsigned long data)
>  			if (ring_idle(ring, seqno)) {
>  				if (waitqueue_active(&ring->irq_queue)) {
>  					/* Issue a wake-up to catch stuck h/w. */
> -					DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
> -						  ring->name);
> -					wake_up_all(&ring->irq_queue);
> -					ring->hangcheck.score += HUNG;
> +					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
> +						DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
> +							  ring->name);
> +						wake_up_all(&ring->irq_queue);
> +					}
> +					/* Safeguard against driver failure */
> +					ring->hangcheck.score += BUSY;
>  				} else
>  					busy = false;
>  			} else {

Honestly, I don't think using the scheduler APIs is a step in the right
direction wrt readability - but I have no better solution, and it seems
to do what you want.

Anyway, I tried to review it, and failed. If you want to split it up
more, I can try again.

Meanwhile, the idea seems okay to me.

-- 
Ben Widawsky, Intel Open Source Technology Center
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