Re: [PATCH v2 3/6] drm/i915: Only track live rings for retiring

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 23/04/2018 19:08, Chris Wilson wrote:
> We don't need to track every ring for its lifetime as they are managed
> by the contexts/engines. What we do want to track are the live rings so
> that we can sporadically clean up requests if userspace falls behind. We
> can simply restrict the gt->rings list to being only gt->live_rings.
> 
> v2: s/live/active/ for consistency with gt.active_requests
> 
> Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/i915_drv.h                  |  3 ++-
>   drivers/gpu/drm/i915/i915_gem.c                  |  6 ++++--
>   drivers/gpu/drm/i915/i915_request.c              | 10 ++++++++--
>   drivers/gpu/drm/i915/intel_ringbuffer.c          |  4 ----
>   drivers/gpu/drm/i915/intel_ringbuffer.h          |  2 +-
>   drivers/gpu/drm/i915/selftests/mock_engine.c     |  4 ----
>   drivers/gpu/drm/i915/selftests/mock_gem_device.c |  5 +++--
>   7 files changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 1837c01d44d0..54351cace362 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2060,7 +2060,8 @@ struct drm_i915_private {
>   
>   		struct i915_gem_timeline global_timeline;
>   		struct list_head timelines;
> -		struct list_head rings;
> +
> +		struct list_head active_rings;
>   		u32 active_requests;
>   		u32 request_serial;
>   
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 906e2395c245..56c79df5ebce 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -141,6 +141,7 @@ static u32 __i915_gem_park(struct drm_i915_private *i915)
>   {
>   	lockdep_assert_held(&i915->drm.struct_mutex);
>   	GEM_BUG_ON(i915->gt.active_requests);
> +	GEM_BUG_ON(!list_empty(&i915->gt.active_rings));
>   
>   	if (!i915->gt.awake)
>   		return I915_EPOCH_INVALID;
> @@ -5599,9 +5600,10 @@ int i915_gem_init_early(struct drm_i915_private *dev_priv)
>   	if (!dev_priv->priorities)
>   		goto err_dependencies;
>   
> -	mutex_lock(&dev_priv->drm.struct_mutex);
> -	INIT_LIST_HEAD(&dev_priv->gt.rings);
>   	INIT_LIST_HEAD(&dev_priv->gt.timelines);
> +	INIT_LIST_HEAD(&dev_priv->gt.active_rings);
> +
> +	mutex_lock(&dev_priv->drm.struct_mutex);
>   	err = i915_gem_timeline_init__global(dev_priv);
>   	mutex_unlock(&dev_priv->drm.struct_mutex);
>   	if (err)
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 0a117bf9e455..f13b7a1a0aa9 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -321,6 +321,7 @@ static void advance_ring(struct i915_request *request)
>   		 * noops - they are safe to be replayed on a reset.
>   		 */
>   		tail = READ_ONCE(request->tail);
> +		list_del(&ring->active_link);
>   	} else {
>   		tail = request->postfix;
>   	}
> @@ -1081,6 +1082,8 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
>   	i915_gem_active_set(&timeline->last_request, request);
>   
>   	list_add_tail(&request->ring_link, &ring->request_list);
> +	if (list_is_first(&request->ring_link, &ring->request_list))
> +		list_add(&ring->active_link, &request->i915->gt.active_rings);

So sneaky.. lets see if it is justified in its new home. :)

>   	request->emitted_jiffies = jiffies;
>   
>   	/*
> @@ -1403,14 +1406,17 @@ static void ring_retire_requests(struct intel_ring *ring)
>   
>   void i915_retire_requests(struct drm_i915_private *i915)
>   {
> -	struct intel_ring *ring, *next;
> +	struct intel_ring *ring, *tmp;
>   
>   	lockdep_assert_held(&i915->drm.struct_mutex);
>   
>   	if (!i915->gt.active_requests)
>   		return;
>   
> -	list_for_each_entry_safe(ring, next, &i915->gt.rings, link)
> +	/* An outstanding request must be on a still active ring somewhere */
> +	GEM_BUG_ON(list_empty(&i915->gt.active_rings));

Okay, but I still think my assert would be stronger. As long as we allow 
calling this function with no active requests, why not check both 
internal states are consistent every time?

> +
> +	list_for_each_entry_safe(ring, tmp, &i915->gt.active_rings, active_link)
>   		ring_retire_requests(ring);
>   }
>   
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 75dca28782ee..3d02b2c779e7 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1149,8 +1149,6 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
>   	}
>   	ring->vma = vma;
>   
> -	list_add(&ring->link, &engine->i915->gt.rings);
> -
>   	return ring;
>   }
>   
> @@ -1162,8 +1160,6 @@ intel_ring_free(struct intel_ring *ring)
>   	i915_vma_close(ring->vma);
>   	__i915_gem_object_release_unless_active(obj);
>   
> -	list_del(&ring->link);
> -
>   	kfree(ring);
>   }
>   
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index d816f8dea245..e8d17bcd9bee 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -129,7 +129,7 @@ struct intel_ring {
>   	void *vaddr;
>   
>   	struct list_head request_list;
> -	struct list_head link;
> +	struct list_head active_link;
>   
>   	u32 head;
>   	u32 tail;
> diff --git a/drivers/gpu/drm/i915/selftests/mock_engine.c b/drivers/gpu/drm/i915/selftests/mock_engine.c
> index a0bc324edadd..74a88913623f 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_engine.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_engine.c
> @@ -140,15 +140,11 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
>   	INIT_LIST_HEAD(&ring->request_list);
>   	intel_ring_update_space(ring);
>   
> -	list_add(&ring->link, &engine->i915->gt.rings);
> -
>   	return ring;
>   }
>   
>   static void mock_ring_free(struct intel_ring *ring)
>   {
> -	list_del(&ring->link);
> -
>   	kfree(ring);
>   }
>   
> diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> index ac4bacf8b5b9..f22a2b35a283 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
> @@ -224,9 +224,10 @@ struct drm_i915_private *mock_gem_device(void)
>   	if (!i915->priorities)
>   		goto err_dependencies;
>   
> -	mutex_lock(&i915->drm.struct_mutex);
> -	INIT_LIST_HEAD(&i915->gt.rings);
>   	INIT_LIST_HEAD(&i915->gt.timelines);
> +	INIT_LIST_HEAD(&i915->gt.active_rings);
> +
> +	mutex_lock(&i915->drm.struct_mutex);
>   	err = i915_gem_timeline_init__global(i915);
>   	if (err) {
>   		mutex_unlock(&i915->drm.struct_mutex);
> 

Regards,

Tvrtko
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