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

[Christian König]

Am 12.02.2018 um 18:14 schrieb Ville Syrjälä:
> 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 at chris-wilson.co.uk>
>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> Cc: Christian Konig <christian.koenig at amd.com>
>> Cc: Dave Airlie <airlied at redhat.com>
> Yep, looks like all of these pass start==1 to idr_alloc().
> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Acked-by: Christian König <christian.koenig at amd.com> as well.

Probably going to do this for the command submission context handles in 
amdgpu as well.

Thanks,
Christian.

>
> 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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