/*
* Copyright © 2017 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*
*/
#include <linux/slab.h>
#include "i915_syncmap.h"
#include "i915_gem.h" /* GEM_BUG_ON() */
#include "i915_selftest.h"
#define SHIFT ilog2(KSYNCMAP)
#define MASK (KSYNCMAP - 1)
/*
* struct i915_syncmap is a layer of a radixtree that maps a u64 fence
* context id to the last u32 fence seqno waited upon from that context.
* Unlike lib/radixtree it uses a parent pointer that allows traversal back to
* the root. This allows us to access the whole tree via a single pointer
* to the most recently used layer. We expect fence contexts to be dense
* and most reuse to be on the same i915_gem_context but on neighbouring
* engines (i.e. on adjacent contexts) and reuse the same leaf, a very
* effective lookup cache. If the new lookup is not on the same leaf, we
* expect it to be on the neighbouring branch.
*
* A leaf holds an array of u32 seqno, and has height 0. The bitmap field
* allows us to store whether a particular seqno is valid (i.e. allows us
* to distinguish unset from 0).
*
* A branch holds an array of layer pointers, and has height > 0, and always
* has at least 2 layers (either branches or leaves) below it.
*
* For example,
* for x in
* 0 1 2 0x10 0x11 0x200 0x201
* 0x500000 0x500001 0x503000 0x503001
* 0xE<<60:
* i915_syncmap_set(&sync, x, lower_32_bits(x));
* will build a tree like:
* 0xXXXXXXXXXXXXXXXX
* 0-> 0x0000000000XXXXXX
* | 0-> 0x0000000000000XXX
* | | 0-> 0x00000000000000XX
* | | | 0-> 0x000000000000000X 0:0, 1:1, 2:2
* | | | 1-> 0x000000000000001X 0:10, 1:11
* | | 2-> 0x000000000000020X 0:200, 1:201
* | 5-> 0x000000000050XXXX
* | 0-> 0x000000000050000X 0:500000, 1:500001
* | 3-> 0x000000000050300X 0:503000, 1:503001
* e-> 0xe00000000000000X e:e
*/
struct i915_syncmap {
u64 prefix;
unsigned int height;
unsigned int bitmap;
struct i915_syncmap *parent;
union {
DECLARE_FLEX_ARRAY(u32, seqno);
DECLARE_FLEX_ARRAY(struct i915_syncmap *, child);
};
};
/**
* i915_syncmap_init -- initialise the #i915_syncmap
* @root: pointer to the #i915_syncmap
*/
void i915_syncmap_init(struct i915_syncmap **root)
{
BUILD_BUG_ON_NOT_POWER_OF_2(KSYNCMAP);
BUILD_BUG_ON_NOT_POWER_OF_2(SHIFT);
BUILD_BUG_ON(KSYNCMAP > BITS_PER_TYPE((*root)->bitmap));
*root = NULL;
}
static inline u32 *__sync_seqno(struct i915_syncmap *p)
{
GEM_BUG_ON(p->height);
return p->seqno;
}
static inline struct i915_syncmap **__sync_child(struct i915_syncmap *p)
{
GEM_BUG_ON(!p->height);
return p->child;
}
static inline unsigned int
__sync_branch_idx(const struct i915_syncmap *p, u64 id)
{
return (id >> p->height) & MASK;
}
static inline unsigned int
__sync_leaf_idx(const struct i915_syncmap *p, u64 id)
{
GEM_BUG_ON(p->height);
return id & MASK;
}
static inline u64 __sync_branch_prefix(const struct i915_syncmap *p, u64 id)
{
return id >> p->height >> SHIFT;
}
static inline u64 __sync_leaf_prefix(const struct i915_syncmap *p, u64 id)
{
GEM_BUG_ON(p->height);
return id >> SHIFT;
}
static inline bool seqno_later(u32 a, u32 b)
{
return (s32)(a - b) >= 0;
}
/**
* i915_syncmap_is_later -- compare against the last know sync point
* @root: pointer to the #i915_syncmap
* @id: the context id (other timeline) we are synchronising to
* @seqno: the sequence number along the other timeline
*
* If we have already synchronised this @root timeline with another (@id) then
* we can omit any repeated or earlier synchronisation requests. If the two
* timelines are already coupled, we can also omit the dependency between the
* two as that is already known via the timeline.
*
* Returns true if the two timelines are already synchronised wrt to @seqno,
* false if not and the synchronisation must be emitted.
*/
bool i915_syncmap_is_later(struct i915_syncmap **root, u64 id, u32 seqno)
{
struct i915_syncmap *p;
unsigned int idx;
p = *root;
if (!p)
return false;
if (likely(__sync_leaf_prefix(p, id) == p->prefix))
goto found;
/* First climb the tree back to a parent branch */
do {
p = p->parent;
if (!p)
return false;
if (__sync_branch_prefix(p, id) == p->prefix)
break;
} while (1);
/* And then descend again until we find our leaf */
do {
if (!p->height)
break;
p = __sync_child(p)[__sync_branch_idx(p, id)];
if (!p)
return false;
if (__sync_branch_prefix(p, id) != p->prefix)
return false;
} while (1);
*root = p;
found:
idx = __sync_leaf_idx(p, id);
if (!(p->bitmap & BIT(idx)))
return false;
return seqno_later(__sync_seqno(p)[idx], seqno);
}
static struct i915_syncmap *
__sync_alloc_leaf(struct i915_syncmap *parent, u64 id)
{
struct i915_syncmap *p;
p = kmalloc(struct_size(p, seqno, KSYNCMAP), GFP_KERNEL);
if (unlikely(!p))
return NULL;
p->parent = parent;
p->height = 0;
p->bitmap = 0;
p->prefix = __sync_leaf_prefix(p, id);
return p;
}
static inline void __sync_set_seqno(struct i915_syncmap *p, u64 id, u32 seqno)
{
unsigned int idx = __sync_leaf_idx(p, id);
p->bitmap |= BIT(idx);
__sync_seqno(p)[idx] = seqno;
}
static inline void __sync_set_child(struct i915_syncmap *p,
unsigned int idx,
struct i915_syncmap *child)
{
p->bitmap |= BIT(idx);
__sync_child(p)[idx] = child;
}
static noinline int __sync_set(struct i915_syncmap **root, u64 id, u32 seqno)
{
struct i915_syncmap *p = *root;
unsigned int idx;
if (!p) {
p = __sync_alloc_leaf(NULL, id);
if (unlikely(!p))
return -ENOMEM;
goto found;
}
/* Caller handled the likely cached case */
GEM_BUG_ON(__sync_leaf_prefix(p, id) == p->prefix);
/* Climb back up the tree until we find a common prefix */
do {
if (!p->parent)
break;
p = p->parent;
if (__sync_branch_prefix(p, id) == p->prefix)
break;
} while (1);
/*
* No shortcut, we have to descend the tree to find the right layer
* containing this fence.
*
* Each layer in the tree holds 16 (KSYNCMAP) pointers, either fences
* or lower layers. Leaf nodes (height = 0) contain the fences, all
* other nodes (height > 0) are internal layers that point to a lower
* node. Each internal layer has at least 2 descendents.
*
* Starting at the top, we check whether the current prefix matches. If
* it doesn't, we have gone past our target and need to insert a join
* into the tree, and a new leaf node for the target as a descendent
* of the join, as well as the original layer.
*
* The matching prefix means we are still following the right branch
* of the tree. If it has height 0, we have found our leaf and just
* need to replace the fence slot with ourselves. If the height is
* not zero, our slot contains the next layer in the tree (unless
* it is empty, in which case we can add ourselves as a new leaf).
* As descend the tree the prefix grows (and height decreases).
*/
do {
struct i915_syncmap *next;
if (__sync_branch_prefix(p, id) != p->prefix) {
unsigned int above;
/* Insert a join above the current layer */
next = kzalloc(struct_size(next, child, KSYNCMAP),
GFP_KERNEL);
if (unlikely(!next))
return -ENOMEM;
/* Compute the height at which these two diverge */
above = fls64(__sync_branch_prefix(p, id) ^ p->prefix);
above = round_up(above, SHIFT);
next->height = above + p->height;
next->prefix = __sync_branch_prefix(next, id);
/* Insert the join into the parent */
if (p->parent) {
idx = __sync_branch_idx(p->parent, id);
__sync_child(p->parent)[idx] = next;
GEM_BUG_ON(!(p->parent->bitmap & BIT(idx)));
}
next->parent = p->parent;
/* Compute the idx of the other branch, not our id! */
idx = p->prefix >> (above - SHIFT) & MASK;
__sync_set_child(next, idx, p);
p->parent = next;
/* Ascend to the join */
p = next;
} else {
if (!p->height)
break;
}
/* Descend into the next layer */
GEM_BUG_ON(!p->height);
idx = __sync_branch_idx(p, id);
next = __sync_child(p)[idx];
if (!next) {
next = __sync_alloc_leaf(p, id);
if (unlikely(!next))
return -ENOMEM;
__sync_set_child(p, idx, next);
p = next;
break;
}
p = next;
} while (1);
found:
GEM_BUG_ON(p->prefix != __sync_leaf_prefix(p, id));
__sync_set_seqno(p, id, seqno);
*root = p;
return 0;
}
/**
* i915_syncmap_set -- mark the most recent syncpoint between contexts
* @root: pointer to the #i915_syncmap
* @id: the context id (other timeline) we have synchronised to
* @seqno: the sequence number along the other timeline
*
* When we synchronise this @root timeline with another (@id), we also know
* that we have synchronized with all previous seqno along that timeline. If
* we then have a request to synchronise with the same seqno or older, we can
* omit it, see i915_syncmap_is_later()
*
* Returns 0 on success, or a negative error code.
*/
int i915_syncmap_set(struct i915_syncmap **root, u64 id, u32 seqno)
{
struct i915_syncmap *p = *root;
/*
* We expect to be called in sequence following is_later(id), which
* should have preloaded the root for us.
*/
if (likely(p && __sync_leaf_prefix(p, id) == p->prefix)) {
__sync_set_seqno(p, id, seqno);
return 0;
}
return __sync_set(root, id, seqno);
}
static void __sync_free(struct i915_syncmap *p)
{
if (p->height) {
unsigned int i;
while ((i = ffs(p->bitmap))) {
p->bitmap &= ~0u << i;
__sync_free(__sync_child(p)[i - 1]);
}
}
kfree(p);
}
/**
* i915_syncmap_free -- free all memory associated with the syncmap
* @root: pointer to the #i915_syncmap
*
* Either when the timeline is to be freed and we no longer need the sync
* point tracking, or when the fences are all known to be signaled and the
* sync point tracking is redundant, we can free the #i915_syncmap to recover
* its allocations.
*
* Will reinitialise the @root pointer so that the #i915_syncmap is ready for
* reuse.
*/
void i915_syncmap_free(struct i915_syncmap **root)
{
struct i915_syncmap *p;
p = *root;
if (!p)
return;
while (p->parent)
p = p->parent;
__sync_free(p);
*root = NULL;
}
#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftests/i915_syncmap.c"
#endif
Codebase Browser
linux