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

Chris Wilson
2018-02-12T14:55:33Z

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>
---
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