Re: [PATCH 04/22] drm/i915: Remove request retirement before each batch

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jul 27, 2016 at 12:14:42PM +0100, Chris Wilson wrote:
> This reimplements the denial-of-service protection against igt from
> commit 227f782e4667 ("drm/i915: Retire requests before creating a new
> one") and transfers the stall from before each batch into get_pages().
> The issue is that the stall is increasing latency between batches which
> is detrimental in some cases (especially coupled with execlists) to
> keeping the GPU well fed. Also we have made the observation that retiring
> requests can of itself free objects (and requests) and therefore makes
> a good first step when shrinking.
> 
> v2: Recycle objects prior to i915_gem_object_get_pages()
> v3: Remove the reference to the ring from i915_gem_requests_ring() as it
> operates on an intel_engine_cs.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h            | 1 -
>  drivers/gpu/drm/i915/i915_gem.c            | 7 +++++--
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 --
>  drivers/gpu/drm/i915/i915_gem_request.c    | 4 ++--
>  4 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index fbda38f25c6b..2de3d16f7b80 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3169,7 +3169,6 @@ struct drm_i915_gem_request *
>  i915_gem_find_active_request(struct intel_engine_cs *engine);
>  
>  void i915_gem_retire_requests(struct drm_i915_private *dev_priv);
> -void i915_gem_retire_requests_ring(struct intel_engine_cs *engine);
>  
>  static inline u32 i915_reset_counter(struct i915_gpu_error *error)
>  {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index bf652dc88024..68dbe4f7940c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2244,7 +2244,6 @@ int
>  i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
> -	const struct drm_i915_gem_object_ops *ops = obj->ops;
>  	int ret;
>  
>  	if (obj->pages)
> @@ -2257,7 +2256,10 @@ i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
>  
>  	BUG_ON(obj->pages_pin_count);
>  
> -	ret = ops->get_pages(obj);
> +	/* Recycle as many active objects as possible first */
> +	i915_gem_retire_requests(dev_priv);
> +
> +	ret = obj->ops->get_pages(obj);

Why exactly do we need this?
- shmem objs already call shrink_all if they can't get at the memory
- everyone else doesn't care.

Even if we need this in some case it looks funny, since it splits the
memory cleanup between caller and callee of get_pages.
-Daniel

>  	if (ret)
>  		return ret;
>  
> @@ -4437,6 +4439,7 @@ i915_gem_cleanup_engines(struct drm_device *dev)
>  static void
>  init_engine_lists(struct intel_engine_cs *engine)
>  {
> +	/* Early initialisation so that core GEM works during engine setup */
>  	INIT_LIST_HEAD(&engine->request_list);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 5e3b5054f72d..0593ea3ba211 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -781,8 +781,6 @@ i915_gem_execbuffer_reserve(struct intel_engine_cs *engine,
>  	bool has_fenced_gpu_access = INTEL_GEN(engine->i915) < 4;
>  	int retry;
>  
> -	i915_gem_retire_requests_ring(engine);
> -
>  	vm = list_first_entry(vmas, struct i915_vma, exec_list)->vm;
>  
>  	INIT_LIST_HEAD(&ordered_vmas);
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 07f08e546915..3395c955a532 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -717,7 +717,7 @@ complete:
>  	return ret;
>  }
>  
> -void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
> +static void engine_retire_requests(struct intel_engine_cs *engine)
>  {
>  	struct drm_i915_gem_request *request, *next;
>  
> @@ -741,7 +741,7 @@ void i915_gem_retire_requests(struct drm_i915_private *dev_priv)
>  	GEM_BUG_ON(!dev_priv->gt.awake);
>  
>  	for_each_engine(engine, dev_priv) {
> -		i915_gem_retire_requests_ring(engine);
> +		engine_retire_requests(engine);
>  		if (list_empty(&engine->request_list))
>  			dev_priv->gt.active_engines &= ~intel_engine_flag(engine);
>  	}
> -- 
> 2.8.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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