[PATCH] drm: Convert prime dma-buf <-> handle to rbtree
David Herrmann
dh.herrmann at gmail.com
Tue Sep 27 06:36:26 UTC 2016
Hi Chris
On Mon, Sep 26, 2016 at 10:44 PM, Chris Wilson <chris at 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 at chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: David Herrmann <dh.herrmann at 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 at gmail.com>
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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