Re: [PATCH 01/10] drm/i915: add interface to simulate gpu hangs

[Ben Widawsky <ben@bwidawsk.net>]

On Fri, 27 Apr 2012 15:17:38 +0200
Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

> gpu reset is a very important piece of our infrastructure.
> Unfortunately we only really it test by actually hanging the gpu,
> which often has bad side-effects for the entire system. And the gpu
> hang handling code is one of the rather complicated pieces of code we
> have, consisting of
> - hang detection
> - error capture
> - actual gpu reset
> - reset of all the gem bookkeeping
> - reinitialition of the entire gpu
> 
> This patch adds a debugfs to selectively stopping rings by ceasing to
> update the hw tail pointer, which will result in the gpu no longer
> updating it's head pointer and eventually to the hangcheck firing.
> This way we can exercise the gpu hang code under controlled conditions
> without a dying gpu taking down the entire systems.

You mean, tail pointer?

> 
> Patch motivated by me forgetting to properly reinitialize ppgtt after
> a gpu reset.
> 
> Usage:
> 
> echo $((1 << $ringnum)) > i915_ring_stop # stops one ring
> 
> echo 0xffffffff > i915_ring_stop # stops all, future-proof version
> 
> then run whatever testload is desired. i915_ring_stop automatically
> resets after a gpu hang is detected to avoid hanging the gpu to fast
> and declaring it wedged.
> 
> v2: Incorporate feedback from Chris Wilson.
> 
> v3: Add the missing cleanup.
> 
> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c     |   65
> +++++++++++++++++++++++++++++++
> drivers/gpu/drm/i915/i915_drv.h         |    2 +
> drivers/gpu/drm/i915/intel_ringbuffer.c |    4 ++ 3 files changed, 71
> insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> b/drivers/gpu/drm/i915/i915_debugfs.c index 120db46..3f6e28e 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1585,6 +1585,64 @@ static const struct file_operations
> i915_wedged_fops = { };
>  
>  static ssize_t
> +i915_ring_stop_read(struct file *filp,
> +		    char __user *ubuf,
> +		    size_t max,
> +		    loff_t *ppos)
> +{
> +	struct drm_device *dev = filp->private_data;
> +	drm_i915_private_t *dev_priv = dev->dev_private;
> +	char buf[80];
> +	int len;
> +
> +	len = snprintf(buf, sizeof(buf),
> +		       "0x%08x\n", dev_priv->stop_rings);
> +
> +	if (len > sizeof(buf))
> +		len = sizeof(buf);
> +
> +	return simple_read_from_buffer(ubuf, max, ppos, buf, len);
> +}
> +
> +static ssize_t
> +i915_ring_stop_write(struct file *filp,
> +		     const char __user *ubuf,
> +		     size_t cnt,
> +		     loff_t *ppos)
> +{
> +	struct drm_device *dev = filp->private_data;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	char buf[20];
> +	int val = 0;
> +
> +	if (cnt > 0) {
> +		if (cnt > sizeof(buf) - 1)
> +			return -EINVAL;
> +
> +		if (copy_from_user(buf, ubuf, cnt))
> +			return -EFAULT;
> +		buf[cnt] = 0;
> +
> +		val = simple_strtoul(buf, NULL, 0);
> +	}
> +
> +	DRM_DEBUG_DRIVER("Stopping rings 0x%08x\n", val);
> +
> +	mutex_lock(&dev->struct_mutex);
> +	dev_priv->stop_rings = val;
> +	mutex_unlock(&dev->struct_mutex);
> +
> +	return cnt;
> +}

Not a huge deal, but I'd go with an interruptible mutex lock there.

Also, I think it would be cool if you did a tail update when going from
!0->0 stop_rings.

> +
> +static const struct file_operations i915_ring_stop_fops = {
> +	.owner = THIS_MODULE,
> +	.open = simple_open,
> +	.read = i915_ring_stop_read,
> +	.write = i915_ring_stop_write,
> +	.llseek = default_llseek,
> +};
> +static ssize_t
>  i915_max_freq_read(struct file *filp,
>  		   char __user *ubuf,
>  		   size_t max,
> @@ -1884,6 +1942,11 @@ int i915_debugfs_init(struct drm_minor *minor)
>  				  &i915_cache_sharing_fops);
>  	if (ret)
>  		return ret;
> +	ret = i915_debugfs_create(minor->debugfs_root, minor,
> +				  "i915_ring_stop",
> +				  &i915_ring_stop_fops);
> +	if (ret)
> +		return ret;
>  
>  	return drm_debugfs_create_files(i915_debugfs_list,
>  					I915_DEBUGFS_ENTRIES,
> @@ -1902,6 +1965,8 @@ void i915_debugfs_cleanup(struct drm_minor
> *minor) 1, minor);
>  	drm_debugfs_remove_files((struct drm_info_list *)
> &i915_cache_sharing_fops, 1, minor);
> +	drm_debugfs_remove_files((struct drm_info_list *)
> &i915_ring_stop_fops,
> +				 1, minor);
>  }
>  
>  #endif /* CONFIG_DEBUG_FS */
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h index 0095c8d..5e62b35 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -413,6 +413,8 @@ typedef struct drm_i915_private {
>  	uint32_t last_instdone;
>  	uint32_t last_instdone1;
>  
> +	unsigned int stop_rings;
> +
>  	unsigned long cfb_size;
>  	unsigned int cfb_fb;
>  	enum plane cfb_plane;
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> b/drivers/gpu/drm/i915/intel_ringbuffer.c index 427b7c5..d2de16d
> 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1221,7 +1221,11 @@ int intel_ring_begin(struct intel_ring_buffer
> *ring, 
>  void intel_ring_advance(struct intel_ring_buffer *ring)
>  {
> +	struct drm_i915_private *dev_priv = ring->dev->dev_private;
> +
>  	ring->tail &= ring->size - 1;
> +	if (dev_priv->stop_rings & intel_ring_flag(ring))
> +		return;
>  	ring->write_tail(ring, ring->tail);
>  }
>