[PATCH v3 1/1] drm/mm: optimize rb_hole_addr rbtree search
Christian König
christian.koenig at amd.com
Mon May 4 13:35:21 UTC 2020
Am 04.05.20 um 12:42 schrieb Nirmoy Das:
> Userspace can severely fragment rb_hole_addr rbtree by manipulating
> alignment while allocating buffers. Fragmented rb_hole_addr rbtree
> would result in large delays while allocating buffer object for a
> userspace application. It takes long time to find suitable hole
> because if we fail to find a suitable hole in the first attempt
> then we look for neighbouring nodes using rb_prev()/rb_next().
> Traversing rbtree using rb_prev()/rb_next() can take really long
> time if the tree is fragmented.
>
> This patch improves searches in fragmented rb_hole_addr rbtree by
> modifying it to an augmented rbtree which will store an extra field
> in drm_mm_node, subtree_max_hole. Each drm_mm_node now stores maximum
> hole size for its subtree in drm_mm_node->subtree_max_hole. Using
> drm_mm_node->subtree_max_hole, it is possible to eliminate complete subtree
"eliminate a complete subtree", but I'm not a native speaker either so
take this with a grain of salt.
> if that subtree is unable to serve a request hence reducing number of
> rb_prev()/rb_next() used.
>
> With this patch applied, 1 million bo allocations on amdgpu took ~8 sec and
"1 million bo allocs on amdgpu took ~8 sec, compared to 50k bo allocs
took 28 sec without".
E.g. keep the numbers in the same order for easy compare.
> without the patch the test code took 28 sec for only 50k bo allocs.
>
> partial test code:
> int test_fragmentation(void)
> {
>
> int i = 0;
> uint32_t minor_version;
> uint32_t major_version;
>
> struct amdgpu_bo_alloc_request request = {};
> amdgpu_bo_handle vram_handle[MAX_ALLOC] = {};
> amdgpu_device_handle device_handle;
>
> request.alloc_size = 4096;
> request.phys_alignment = 8192;
> request.preferred_heap = AMDGPU_GEM_DOMAIN_VRAM;
>
> int fd = open("/dev/dri/card0", O_RDWR | O_CLOEXEC);
> amdgpu_device_initialize(fd, &major_version, &minor_version,
> &device_handle);
>
> for (i = 0; i < MAX_ALLOC; i++) {
> amdgpu_bo_alloc(device_handle, &request, &vram_handle[i]);
> }
>
> for (i = 0; i < MAX_ALLOC; i++)
> amdgpu_bo_free(vram_handle[i]);
>
> return 0;
> }
>
> v2:
> Use RB_DECLARE_CALLBACKS_MAX to maintain subtree_max_hole
> v3:
> insert_hole_addr() should be static a function
> fix return value of next_hole_high_addr()/next_hole_low_addr()
> Reported-by: kbuild test robot <lkp at intel.com>
>
> Signed-off-by: Nirmoy Das <nirmoy.das at amd.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
> drivers/gpu/drm/drm_mm.c | 133 +++++++++++++++++++++++++++++++++------
> include/drm/drm_mm.h | 1 +
> 2 files changed, 115 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> index 8981abe8b7c9..f4ca1ff80af9 100644
> --- a/drivers/gpu/drm/drm_mm.c
> +++ b/drivers/gpu/drm/drm_mm.c
> @@ -212,20 +212,6 @@ static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
> &drm_mm_interval_tree_augment);
> }
>
> -#define RB_INSERT(root, member, expr) do { \
> - struct rb_node **link = &root.rb_node, *rb = NULL; \
> - u64 x = expr(node); \
> - while (*link) { \
> - rb = *link; \
> - if (x < expr(rb_entry(rb, struct drm_mm_node, member))) \
> - link = &rb->rb_left; \
> - else \
> - link = &rb->rb_right; \
> - } \
> - rb_link_node(&node->member, rb, link); \
> - rb_insert_color(&node->member, &root); \
> -} while (0)
> -
> #define HOLE_SIZE(NODE) ((NODE)->hole_size)
> #define HOLE_ADDR(NODE) (__drm_mm_hole_node_start(NODE))
>
> @@ -255,16 +241,42 @@ static void insert_hole_size(struct rb_root_cached *root,
> rb_insert_color_cached(&node->rb_hole_size, root, first);
> }
>
> +RB_DECLARE_CALLBACKS_MAX(static, augment_callbacks,
> + struct drm_mm_node, rb_hole_addr,
> + u64, subtree_max_hole, HOLE_SIZE)
Well that is a really nice solution. I've reviewed the implementation
and couldn't find anything obvious wrong.
But I'm neither an expert on the drm_mm code nor the augmented RB tree
implementation. So Acked-by: Christian König <christian.koenig at amd.com>
for this patch.
As a follow up I think we should extend this into keeping track of
subtree_max_hole_align. With HOLE_SIZE_ALIGN(NODE) defined as
(((NODE)->hole_size) << 6) | ffs(HOLE_ADDR(NODE)).
This way we can also handle the ugly case of 4K allocation which are 8K
aligned.
Regards,
Christian.
> +
> +static void insert_hole_addr(struct rb_root *root, struct drm_mm_node *node)
> +{
> + struct rb_node **link = &root->rb_node, *rb_parent = NULL;
> + u64 start = HOLE_ADDR(node), subtree_max_hole = node->subtree_max_hole;
> + struct drm_mm_node *parent;
> +
> + while (*link) {
> + rb_parent = *link;
> + parent = rb_entry(rb_parent, struct drm_mm_node, rb_hole_addr);
> + if (parent->subtree_max_hole < subtree_max_hole)
> + parent->subtree_max_hole = subtree_max_hole;
> + if (start < HOLE_ADDR(parent))
> + link = &parent->rb_hole_addr.rb_left;
> + else
> + link = &parent->rb_hole_addr.rb_right;
> + }
> +
> + rb_link_node(&node->rb_hole_addr, rb_parent, link);
> + rb_insert_augmented(&node->rb_hole_addr, root, &augment_callbacks);
> +}
> +
> static void add_hole(struct drm_mm_node *node)
> {
> struct drm_mm *mm = node->mm;
>
> node->hole_size =
> __drm_mm_hole_node_end(node) - __drm_mm_hole_node_start(node);
> + node->subtree_max_hole = node->hole_size;
> DRM_MM_BUG_ON(!drm_mm_hole_follows(node));
>
> insert_hole_size(&mm->holes_size, node);
> - RB_INSERT(mm->holes_addr, rb_hole_addr, HOLE_ADDR);
> + insert_hole_addr(&mm->holes_addr, node);
>
> list_add(&node->hole_stack, &mm->hole_stack);
> }
> @@ -275,8 +287,10 @@ static void rm_hole(struct drm_mm_node *node)
>
> list_del(&node->hole_stack);
> rb_erase_cached(&node->rb_hole_size, &node->mm->holes_size);
> - rb_erase(&node->rb_hole_addr, &node->mm->holes_addr);
> + rb_erase_augmented(&node->rb_hole_addr, &node->mm->holes_addr,
> + &augment_callbacks);
> node->hole_size = 0;
> + node->subtree_max_hole = 0;
>
> DRM_MM_BUG_ON(drm_mm_hole_follows(node));
> }
> @@ -361,9 +375,90 @@ first_hole(struct drm_mm *mm,
> }
> }
>
> +/**
> + * next_hole_high_addr - returns next hole for a DRM_MM_INSERT_HIGH mode request
> + * @entry: previously selected drm_mm_node
> + * @size: size of the a hole needed for the request
> + *
> + * This function will verify whether left subtree of @entry has hole big enough
> + * to fit the requtested size. If so, it will return previous node of @entry or
> + * else it will return parent node of @entry
> + *
> + * It will also skip the complete left subtree if subtree_max_hole of that
> + * subtree is same as the subtree_max_hole of the @entry.
> + *
> + * Returns:
> + * previous node of @entry if left subtree of @entry can serve the request or
> + * else return parent of @entry
> + */
> +static struct drm_mm_node *
> +next_hole_high_addr(struct drm_mm_node *entry, u64 size)
> +{
> + struct rb_node *rb_node, *left_rb_node, *parent_rb_node;
> + struct drm_mm_node *left_node;
> +
> + if (!entry)
> + return NULL;
> +
> + rb_node = &entry->rb_hole_addr;
> + if (rb_node->rb_left) {
> + left_rb_node = rb_node->rb_left;
> + parent_rb_node = rb_parent(rb_node);
> + left_node = rb_entry(left_rb_node,
> + struct drm_mm_node, rb_hole_addr);
> + if ((left_node->subtree_max_hole < size ||
> + entry->size == entry->subtree_max_hole) &&
> + parent_rb_node && parent_rb_node->rb_left != rb_node)
> + return rb_hole_addr_to_node(parent_rb_node);
> + }
> +
> + return rb_hole_addr_to_node(rb_prev(rb_node));
> +}
> +
> +/**
> + * next_hole_low_addr - returns next hole for a DRM_MM_INSERT_LOW mode request
> + * @entry: previously selected drm_mm_node
> + * @size: size of the a hole needed for the request
> + *
> + * This function will verify whether right subtree of @entry has hole big enough
> + * to fit the requtested size. If so, it will return next node of @entry or
> + * else it will return parent node of @entry
> + *
> + * It will also skip the complete right subtree if subtree_max_hole of that
> + * subtree is same as the subtree_max_hole of the @entry.
> + *
> + * Returns:
> + * next node of @entry if right subtree of @entry can serve the request or
> + * else return parent of @entry
> + */
> +static struct drm_mm_node *
> +next_hole_low_addr(struct drm_mm_node *entry, u64 size)
> +{
> + struct rb_node *rb_node, *right_rb_node, *parent_rb_node;
> + struct drm_mm_node *right_node;
> +
> + if (!entry)
> + return NULL;
> +
> + rb_node = &entry->rb_hole_addr;
> + if (rb_node->rb_right) {
> + right_rb_node = rb_node->rb_right;
> + parent_rb_node = rb_parent(rb_node);
> + right_node = rb_entry(right_rb_node,
> + struct drm_mm_node, rb_hole_addr);
> + if ((right_node->subtree_max_hole < size ||
> + entry->size == entry->subtree_max_hole) &&
> + parent_rb_node && parent_rb_node->rb_right != rb_node)
> + return rb_hole_addr_to_node(parent_rb_node);
> + }
> +
> + return rb_hole_addr_to_node(rb_next(rb_node));
> +}
> +
> static struct drm_mm_node *
> next_hole(struct drm_mm *mm,
> struct drm_mm_node *node,
> + u64 size,
> enum drm_mm_insert_mode mode)
> {
> switch (mode) {
> @@ -372,10 +467,10 @@ next_hole(struct drm_mm *mm,
> return rb_hole_size_to_node(rb_prev(&node->rb_hole_size));
>
> case DRM_MM_INSERT_LOW:
> - return rb_hole_addr_to_node(rb_next(&node->rb_hole_addr));
> + return next_hole_low_addr(node, size);
>
> case DRM_MM_INSERT_HIGH:
> - return rb_hole_addr_to_node(rb_prev(&node->rb_hole_addr));
> + return next_hole_high_addr(node, size);
>
> case DRM_MM_INSERT_EVICT:
> node = list_next_entry(node, hole_stack);
> @@ -489,7 +584,7 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm,
> remainder_mask = is_power_of_2(alignment) ? alignment - 1 : 0;
> for (hole = first_hole(mm, range_start, range_end, size, mode);
> hole;
> - hole = once ? NULL : next_hole(mm, hole, mode)) {
> + hole = once ? NULL : next_hole(mm, hole, size, mode)) {
> u64 hole_start = __drm_mm_hole_node_start(hole);
> u64 hole_end = hole_start + hole->hole_size;
> u64 adj_start, adj_end;
> diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
> index ee8b0e80ca90..a01bc6fac83c 100644
> --- a/include/drm/drm_mm.h
> +++ b/include/drm/drm_mm.h
> @@ -168,6 +168,7 @@ struct drm_mm_node {
> struct rb_node rb_hole_addr;
> u64 __subtree_last;
> u64 hole_size;
> + u64 subtree_max_hole;
> unsigned long flags;
> #define DRM_MM_NODE_ALLOCATED_BIT 0
> #define DRM_MM_NODE_SCANNED_BIT 1
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