[Intel-gfx] [PATCH 079/190] drm/i915: Reduce the pointer dance of i915_is_ggtt()

[Dave Gordon]

On 11/01/16 09:17, Chris Wilson wrote:
> The multiple levels of indirect do nothing but hinder the compiler and
> the pointer chasing turns to be quite painful but painless to fix.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c        | 13 ++++++-------
>   drivers/gpu/drm/i915/i915_drv.h            |  7 -------
>   drivers/gpu/drm/i915/i915_gem.c            | 18 +++++++-----------
>   drivers/gpu/drm/i915/i915_gem_execbuffer.c |  5 ++---
>   drivers/gpu/drm/i915/i915_gem_gtt.c        | 12 +++++-------
>   drivers/gpu/drm/i915/i915_gem_gtt.h        |  5 +++++
>   drivers/gpu/drm/i915/i915_trace.h          | 27 ++++++++-------------------
>   7 files changed, 33 insertions(+), 54 deletions(-)

[snip]

> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c9c1a5cdc1e5..f840cc55f1ab 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2905,18 +2905,11 @@ bool i915_gem_obj_is_pinned(struct drm_i915_gem_object *obj);
>   /* Some GGTT VM helpers */
>   #define i915_obj_to_ggtt(obj) \
>   	(&((struct drm_i915_private *)(obj)->base.dev->dev_private)->gtt.base)
> -static inline bool i915_is_ggtt(struct i915_address_space *vm)
> -{
> -	struct i915_address_space *ggtt =
> -		&((struct drm_i915_private *)(vm)->dev->dev_private)->gtt.base;
> -	return vm == ggtt;
> -}

> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index b5c3bbe6dc2a..06117bd0fc00 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -3150,6 +3150,7 @@ int i915_gem_gtt_init(struct drm_device *dev)
>   	}
>
>   	gtt->base.dev = dev;
> +	gtt->base.is_ggtt = true;

So, it looks like the plan here is that when we need to determine 
whether something is the special distinguished instance of a type, then 
instead of comparing its address against the global pointer to the 
distinguished instance, we'll just look for a flag /inside/ the object 
itself, which is set /only/ on the distinguished instance.

Now why didn't I think of that? That looks like such a good idea, we 
should apply it in other CONTEXTs!

Reviewed-by: Dave Gordon <david.s.gordon at intel.com>