Re: [PATCH] drm: Use idr_init_base(1) when using id==0 for invalid

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 12, 2018 at 02:55:33PM +0000, Chris Wilson wrote:
> Use the new idr_init_base() function to create an IDR that knows id==0
> is never allocated as it maps to an invalid identifier. By knowing that
> id==0 is invalid, the IDR can start from id=1 instead avoiding the issue
> of having to start each lookup from the zeroth leaf as id==0 is always
> unused (and thus the tree-of-bitmaps indicate that is the first
> available).
> 
> References: 6ce711f27500 ("idr: Make 1-based IDRs more efficient")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Christian Konig <christian.koenig@amd.com>
> Cc: Dave Airlie <airlied@redhat.com>

Yep, looks like all of these pass start==1 to idr_alloc().
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Looks like at least tile_idr and crtc_idr could use this as well,
although I suppose they're not hit nearly as hard as the gem stuff.
Also someone should really s/crtc_idr/obj_id_idr/ or something
along those lines.

> ---
> Note this requires 4.16-rc1.
> ---
>  drivers/gpu/drm/drm_gem.c     | 4 ++--
>  drivers/gpu/drm/drm_syncobj.c | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 01f8d9481211..4975ba9a7bc8 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -98,7 +98,7 @@ drm_gem_init(struct drm_device *dev)
>  	struct drm_vma_offset_manager *vma_offset_manager;
>  
>  	mutex_init(&dev->object_name_lock);
> -	idr_init(&dev->object_name_idr);
> +	idr_init_base(&dev->object_name_idr, 1);
>  
>  	vma_offset_manager = kzalloc(sizeof(*vma_offset_manager), GFP_KERNEL);
>  	if (!vma_offset_manager) {
> @@ -776,7 +776,7 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data,
>  void
>  drm_gem_open(struct drm_device *dev, struct drm_file *file_private)
>  {
> -	idr_init(&file_private->object_idr);
> +	idr_init_base(&file_private->object_idr, 1);
>  	spin_lock_init(&file_private->table_lock);
>  }
>  
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 0b7b0d1ad2d5..d4f4ce484529 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -546,7 +546,7 @@ static int drm_syncobj_export_sync_file(struct drm_file *file_private,
>  void
>  drm_syncobj_open(struct drm_file *file_private)
>  {
> -	idr_init(&file_private->syncobj_idr);
> +	idr_init_base(&file_private->syncobj_idr, 1);
>  	spin_lock_init(&file_private->syncobj_table_lock);
>  }
>  
> -- 
> 2.16.1
> 
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-- 
Ville Syrjälä
Intel OTC
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