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drm/mm: optimize rb_hole_addr rbtree search

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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 a complete
subtree 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 allocs on amdgpu took ~8 sec,
compared to 50k bo allocs which took 28 sec without it.

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@intel.com>
v4:
Fix commit message.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/364341/
Signed-off-by: Christian König <christian.koenig@amd.com>
This commit is contained in:
Nirmoy Das 2020-05-04 17:40:35 +02:00 committed by Christian König
parent b7301fd812
commit 0cdea4455a
2 changed files with 115 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

133
drivers/gpu/drm/drm_mm.c
View file

@ -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)
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;

1
include/drm/drm_mm.h
View file

@ -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