[Intel-gfx] [PATCH 04/38] drm/i915: Remove request retirement before each batch

[Mika Kuoppala]

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

> [ text/plain ]
> This reimplements the denial-of-service protection against igt from
>
> commit 227f782e4667fc622810bce8be8ccdeee45f89c2
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date:   Thu May 15 10:41:42 2014 +0100
>
>     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. 

I didn't check the claims about the latency benefits, but
overall the retiring when we need the pages instead
of retiring on each execbuffer makes sense to me, so

Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com>

>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()
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h            | 1 -
>  drivers/gpu/drm/i915/i915_gem.c            | 9 ++++++---
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 --
>  drivers/gpu/drm/i915/i915_gem_request.c    | 2 +-
>  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 09f6f0eecd96..a065325580d8 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3065,7 +3065,6 @@ 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 a7aa465cb76d..19b8d2ea7698 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1989,8 +1989,7 @@ err_pages:
>  int
>  i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
>  {
> -	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
> -	const struct drm_i915_gem_object_ops *ops = obj->ops;
> +	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
>  	int ret;
>  
>  	if (obj->pages)
> @@ -2003,7 +2002,10 @@ 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);
>  	if (ret)
>  		return ret;
>  
> @@ -4161,6 +4163,7 @@ 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 7b381358512e..1b19a36adedc 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -751,8 +751,6 @@ 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 38e5daecd8f5..59afc8e547c4 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -734,7 +734,7 @@ int i915_wait_request(struct drm_i915_gem_request *req)
>  	return 0;
>  }
>  
> -void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
> +static void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
>  {
>  	struct drm_i915_gem_request *request, *next;
>  
> -- 
> 2.8.1
>
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