Re: [PATCH] drm: Convert prime dma-buf <-> handle to rbtree

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Sep 27, 2016 at 12:18:13PM -0400, Sean Paul wrote:
> On Tue, Sep 27, 2016 at 2:36 AM, David Herrmann <dh.herrmann@gmail.com> wrote:
> > Hi Chris
> >
> > On Mon, Sep 26, 2016 at 10:44 PM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> >> Currently we use a linear walk to lookup a handle and return a dma-buf,
> >> and vice versa. A long overdue TODO task is to convert that to a
> >> hashtable. Since the initial implementation of dma-buf/prime, we now
> >> have resizeable hashtables we can use (and now a future task is to RCU
> >> enable the lookup!). However, this patch opts to use an rbtree instead
> >> to provide O(lgN) lookups (and insertion, deletion). rbtrees were chosen
> >> over using the RCU backed resizable hashtable to firstly avoid the
> >> reallocations (rbtrees can be embedded entirely within the parent
> >> struct) and to favour simpler code with predictable worst case
> >> behaviour. In simple testing, the difference between using the constant
> >> lookup and insertion of the rhashtable and the rbtree was less than 10%
> >> of the wall time (igt/benchmarks/prime_lookup) - both are dramatic
> >> improvements over the existing linear lists.
> >>
> >> v2: Favour rbtree over rhashtable
> >>
> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94631
> >> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >> Cc: Sean Paul <seanpaul@chromium.org>
> >> Cc: David Herrmann <dh.herrmann@gmail.com>
> >> ---
> >>  drivers/gpu/drm/drm_prime.c | 85 +++++++++++++++++++++++++++++++++++++++------
> >>  include/drm/drmP.h          |  5 +--
> >>  2 files changed, 77 insertions(+), 13 deletions(-)
> >
> > Thanks for doing the benchmark and rewriting it with rb-trees. I think
> > the lack of error-handling is a big plus here. Anyway, this is:
> >
> > Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
> 
> 
> Agreed, it's also nice be able to keep the WARN_ON in
> drm_prime_destroy_file_private
> 
> Reviewed-by: Sean Paul <seanpaul@chromium.org>

Applied to drm-misc, thanks.
-Daniel

> 
> >
> > Your tree-traversals are a bit inconsistent in how you order your
> > iterator against the element to lookup in your conditions, but.. meh.
> > A big WARN_ON on conflicts might not hurt either. But looks all good.
> >
> > Thanks
> > David
> >
> >> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> >> index 780589b420a4..57201d68cf61 100644
> >> --- a/drivers/gpu/drm/drm_prime.c
> >> +++ b/drivers/gpu/drm/drm_prime.c
> >> @@ -28,6 +28,7 @@
> >>
> >>  #include <linux/export.h>
> >>  #include <linux/dma-buf.h>
> >> +#include <linux/rbtree.h>
> >>  #include <drm/drmP.h>
> >>  #include <drm/drm_gem.h>
> >>
> >> @@ -61,9 +62,11 @@
> >>   */
> >>
> >>  struct drm_prime_member {
> >> -       struct list_head entry;
> >>         struct dma_buf *dma_buf;
> >>         uint32_t handle;
> >> +
> >> +       struct rb_node dmabuf_rb;
> >> +       struct rb_node handle_rb;
> >>  };
> >>
> >>  struct drm_prime_attachment {
> >> @@ -75,6 +78,7 @@ static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
> >>                                     struct dma_buf *dma_buf, uint32_t handle)
> >>  {
> >>         struct drm_prime_member *member;
> >> +       struct rb_node **p, *rb;
> >>
> >>         member = kmalloc(sizeof(*member), GFP_KERNEL);
> >>         if (!member)
> >> @@ -83,18 +87,56 @@ static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
> >>         get_dma_buf(dma_buf);
> >>         member->dma_buf = dma_buf;
> >>         member->handle = handle;
> >> -       list_add(&member->entry, &prime_fpriv->head);
> >> +
> >> +       rb = NULL;
> >> +       p = &prime_fpriv->dmabufs.rb_node;
> >> +       while (*p) {
> >> +               struct drm_prime_member *pos;
> >> +
> >> +               rb = *p;
> >> +               pos = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
> >> +               if (dma_buf > pos->dma_buf)
> >> +                       p = &rb->rb_right;
> >> +               else
> >> +                       p = &rb->rb_left;
> >> +       }
> >> +       rb_link_node(&member->dmabuf_rb, rb, p);
> >> +       rb_insert_color(&member->dmabuf_rb, &prime_fpriv->dmabufs);
> >> +
> >> +       rb = NULL;
> >> +       p = &prime_fpriv->handles.rb_node;
> >> +       while (*p) {
> >> +               struct drm_prime_member *pos;
> >> +
> >> +               rb = *p;
> >> +               pos = rb_entry(rb, struct drm_prime_member, handle_rb);
> >> +               if (handle > pos->handle)
> >> +                       p = &rb->rb_right;
> >> +               else
> >> +                       p = &rb->rb_left;
> >> +       }
> >> +       rb_link_node(&member->handle_rb, rb, p);
> >> +       rb_insert_color(&member->handle_rb, &prime_fpriv->handles);
> >> +
> >>         return 0;
> >>  }
> >>
> >>  static struct dma_buf *drm_prime_lookup_buf_by_handle(struct drm_prime_file_private *prime_fpriv,
> >>                                                       uint32_t handle)
> >>  {
> >> -       struct drm_prime_member *member;
> >> +       struct rb_node *rb;
> >> +
> >> +       rb = prime_fpriv->handles.rb_node;
> >> +       while (rb) {
> >> +               struct drm_prime_member *member;
> >>
> >> -       list_for_each_entry(member, &prime_fpriv->head, entry) {
> >> +               member = rb_entry(rb, struct drm_prime_member, handle_rb);
> >>                 if (member->handle == handle)
> >>                         return member->dma_buf;
> >> +               else if (member->handle < handle)
> >> +                       rb = rb->rb_right;
> >> +               else
> >> +                       rb = rb->rb_left;
> >>         }
> >>
> >>         return NULL;
> >> @@ -104,14 +146,23 @@ static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpri
> >>                                        struct dma_buf *dma_buf,
> >>                                        uint32_t *handle)
> >>  {
> >> -       struct drm_prime_member *member;
> >> +       struct rb_node *rb;
> >> +
> >> +       rb = prime_fpriv->dmabufs.rb_node;
> >> +       while (rb) {
> >> +               struct drm_prime_member *member;
> >>
> >> -       list_for_each_entry(member, &prime_fpriv->head, entry) {
> >> +               member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
> >>                 if (member->dma_buf == dma_buf) {
> >>                         *handle = member->handle;
> >>                         return 0;
> >> +               } else if (member->dma_buf < dma_buf) {
> >> +                       rb = rb->rb_right;
> >> +               } else {
> >> +                       rb = rb->rb_left;
> >>                 }
> >>         }
> >> +
> >>         return -ENOENT;
> >>  }
> >>
> >> @@ -166,13 +217,24 @@ static void drm_gem_map_detach(struct dma_buf *dma_buf,
> >>  void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv,
> >>                                         struct dma_buf *dma_buf)
> >>  {
> >> -       struct drm_prime_member *member, *safe;
> >> +       struct rb_node *rb;
> >>
> >> -       list_for_each_entry_safe(member, safe, &prime_fpriv->head, entry) {
> >> +       rb = prime_fpriv->dmabufs.rb_node;
> >> +       while (rb) {
> >> +               struct drm_prime_member *member;
> >> +
> >> +               member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
> >>                 if (member->dma_buf == dma_buf) {
> >> +                       rb_erase(&member->handle_rb, &prime_fpriv->handles);
> >> +                       rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
> >> +
> >>                         dma_buf_put(dma_buf);
> >> -                       list_del(&member->entry);
> >>                         kfree(member);
> >> +                       return;
> >> +               } else if (member->dma_buf < dma_buf) {
> >> +                       rb = rb->rb_right;
> >> +               } else {
> >> +                       rb = rb->rb_left;
> >>                 }
> >>         }
> >>  }
> >> @@ -759,12 +821,13 @@ EXPORT_SYMBOL(drm_prime_gem_destroy);
> >>
> >>  void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)
> >>  {
> >> -       INIT_LIST_HEAD(&prime_fpriv->head);
> >>         mutex_init(&prime_fpriv->lock);
> >> +       prime_fpriv->dmabufs = RB_ROOT;
> >> +       prime_fpriv->handles = RB_ROOT;
> >>  }
> >>
> >>  void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
> >>  {
> >>         /* by now drm_gem_release should've made sure the list is empty */
> >> -       WARN_ON(!list_empty(&prime_fpriv->head));
> >> +       WARN_ON(!RB_EMPTY_ROOT(&prime_fpriv->dmabufs));
> >>  }
> >> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> >> index c53dc90942e0..289207f12adb 100644
> >> --- a/include/drm/drmP.h
> >> +++ b/include/drm/drmP.h
> >> @@ -51,6 +51,7 @@
> >>  #include <linux/platform_device.h>
> >>  #include <linux/poll.h>
> >>  #include <linux/ratelimit.h>
> >> +#include <linux/rbtree.h>
> >>  #include <linux/sched.h>
> >>  #include <linux/slab.h>
> >>  #include <linux/types.h>
> >> @@ -371,10 +372,10 @@ struct drm_pending_event {
> >>                       we deliver the event, for tracing only */
> >>  };
> >>
> >> -/* initial implementaton using a linked list - todo hashtab */
> >>  struct drm_prime_file_private {
> >> -       struct list_head head;
> >>         struct mutex lock;
> >> +       struct rb_root dmabufs;
> >> +       struct rb_root handles;
> >>  };
> >>
> >>  /** File private data */
> >> --
> >> 2.9.3
> >>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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