On Thu, Jun 29, 2017 at 01:59:30PM +0100, Chris Wilson wrote:
> Reduce the list iteration when incrementing the timeline by storing the
> fences in increasing order.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
> ---
> drivers/dma-buf/sw_sync.c | 49 ++++++++++++++++++++++++++++++++++++++------
> drivers/dma-buf/sync_debug.h | 5 +++++
> 2 files changed, 48 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> index e51fe11bbbea..8cef5d345316 100644
> --- a/drivers/dma-buf/sw_sync.c
> +++ b/drivers/dma-buf/sw_sync.c
> @@ -96,6 +96,7 @@ static struct sync_timeline *sync_timeline_create(const char *name)
> obj->context = dma_fence_context_alloc(1);
> strlcpy(obj->name, name, sizeof(obj->name));
>
> + obj->pt_tree = RB_ROOT;
> INIT_LIST_HEAD(&obj->pt_list);
> spin_lock_init(&obj->lock);
>
> @@ -142,9 +143,13 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)
>
> obj->value += inc;
>
> - list_for_each_entry_safe(pt, next, &obj->pt_list, link)
> - if (dma_fence_is_signaled_locked(&pt->base))
> - list_del_init(&pt->link);
> + list_for_each_entry_safe(pt, next, &obj->pt_list, link) {
> + if (!dma_fence_is_signaled_locked(&pt->base))
> + break;
> +
> + list_del_init(&pt->link);
> + rb_erase(&pt->node, &obj->pt_tree);
> + }
>
> spin_unlock_irq(&obj->lock);
> }
> @@ -174,8 +179,38 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj,
> INIT_LIST_HEAD(&pt->link);
>
> spin_lock_irq(&obj->lock);
> - if (!dma_fence_is_signaled_locked(&pt->base))
> - list_add_tail(&pt->link, &obj->pt_list);
> + if (!dma_fence_is_signaled_locked(&pt->base)) {
> + struct rb_node **p = &obj->pt_tree.rb_node;
> + struct rb_node *parent = NULL;
> +
> + while (*p) {
> + struct sync_pt *other;
> + int cmp;
> +
> + parent = *p;
> + other = rb_entry(parent, typeof(*pt), node);
> + cmp = value - other->base.seqno;
We're imposing an implicit limitation on userspace here that points cannot be
> INT_MAX apart (since they'll be in the wrong order in the tree).
I wonder how much this patch will actually save, given that the number of active points
on a given timeline should be small. Do we have any evidence that this
optimization is warranted?
Sean
> + if (cmp > 0) {
> + p = &parent->rb_right;
> + } else if (cmp < 0) {
> + p = &parent->rb_left;
> + } else {
> + if (dma_fence_get_rcu(&other->base)) {
> + dma_fence_put(&pt->base);
> + pt = other;
> + goto unlock;
> + }
> + p = &parent->rb_left;
> + }
> + }
> + rb_link_node(&pt->node, parent, p);
> + rb_insert_color(&pt->node, &obj->pt_tree);
> +
> + parent = rb_next(&pt->node);
> + list_add_tail(&pt->link,
> + parent ? &rb_entry(parent, typeof(*pt), node)->link : &obj->pt_list);
> + }
> +unlock:
> spin_unlock_irq(&obj->lock);
>
> return pt;
> @@ -201,8 +236,10 @@ static void timeline_fence_release(struct dma_fence *fence)
>
> spin_lock_irqsave(fence->lock, flags);
>
> - if (!list_empty(&pt->link))
> + if (!list_empty(&pt->link)) {
> list_del(&pt->link);
> + rb_erase(&pt->node, &parent->pt_tree);
> + }
>
> spin_unlock_irqrestore(fence->lock, flags);
>
> diff --git a/drivers/dma-buf/sync_debug.h b/drivers/dma-buf/sync_debug.h
> index 899ba0e19fd3..b7a5fab12179 100644
> --- a/drivers/dma-buf/sync_debug.h
> +++ b/drivers/dma-buf/sync_debug.h
> @@ -14,6 +14,7 @@
> #define _LINUX_SYNC_H
>
> #include <linux/list.h>
> +#include <linux/rbtree.h>
> #include <linux/spinlock.h>
> #include <linux/dma-fence.h>
>
> @@ -25,6 +26,7 @@
> * @kref: reference count on fence.
> * @name: name of the sync_timeline. Useful for debugging
> * @lock: lock protecting @child_list_head and fence.status
> + * @pt_tree: rbtree of active (unsignaled/errored) sync_pts
> * @pt_list: list of active (unsignaled/errored) sync_pts
> * @sync_timeline_list: membership in global sync_timeline_list
> */
> @@ -36,6 +38,7 @@ struct sync_timeline {
> u64 context;
> int value;
>
> + struct rb_root pt_tree;
> struct list_head pt_list;
> spinlock_t lock;
>
> @@ -51,10 +54,12 @@ static inline struct sync_timeline *dma_fence_parent(struct dma_fence *fence)
> * struct sync_pt - sync_pt object
> * @base: base fence object
> * @link: link on the sync timeline's list
> + * @node: node in the sync timeline's tree
> */
> struct sync_pt {
> struct dma_fence base;
> struct list_head link;
> + struct rb_node node;
> };
>
> #ifdef CONFIG_SW_SYNC
> --
> 2.13.1
--
Sean Paul, Software Engineer, Google / Chromium OS
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