1 files changed, 127 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/common/mm/lockless_allocator_priv.h b/drivers/gpu/nvgpu/common/mm/lockless_allocator_priv.h
new file mode 100644
index 00000000..c2f6649a
--- /dev/null
+++ b/drivers/gpu/nvgpu/common/mm/lockless_allocator_priv.h
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2016 - 2017, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * 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 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.
+ */
+
+/*
+ * Basics:
+ *
+ *    - Lockless memory allocator for fixed-size structures, whose
+ *      size is defined up front at init time.
+ *    - Memory footprint scales linearly w/ the number of structures in
+ *      the pool. It is ~= sizeof(int) * N.
+ *    - Memory is pre-allocated by the client. The allocator itself
+ *      only computes the addresses for allocations.
+ *    - Limit of MAX_INT nodes that the allocator can be responsible for.
+ *
+ * Implementation details:
+ *
+ *    The allocator maintains a single list of free nodes. We allocate &
+ *    free nodes from the head of the list. We rely on the cmpxchg() operator
+ *    to maintain atomicity on the head.
+ *
+ *    So, both allocs & frees are O(1)!!
+ *
+ *    -- Definitions --
+ *    Block Size - size of a single structure that this allocator will
+ *                 allocate.
+ *    Node       - one of the elements of size blk_size in the
+ *                 client-allocated buffer.
+ *    Node Index - zero-based index of a node in the client-allocated
+ *                 contiguous buffer.
+ *
+ *    -- Initial State --
+ *    We maintain the following to track the state of the free list:
+ *
+ *    1) A "head" index to track the index of the first free node in the list
+ *    2) A "next" array to track the index of the next free node in the list
+ *       for every node. So next[head], will give the index to the 2nd free
+ *       element in the list.
+ *
+ *    So, to begin with, the free list consists of all node indices, and each
+ *    position in the next array contains index N + 1:
+ *
+ *    head = 0
+ *    next = [1, 2, 3, 4, -1] : Example for a user-allocated buffer of 5 nodes
+ *    free_list = 0->1->2->3->4->-1
+ *
+ *    -- Allocations --
+ *    1) Read the current head (aka acq_head)
+ *    2) Read next[acq_head], to get the 2nd free element (aka new_head)
+ *    3) cmp_xchg(&head, acq_head, new_head)
+ *    4) If it succeeds, compute the address of the node, based on
+ *       base address, blk_size, & acq_head.
+ *
+ *    head = 1;
+ *    next = [1, 2, 3, 4, -1] : Example after allocating Node #0
+ *    free_list = 1->2->3->4->-1
+ *
+ *    head = 2;
+ *    next = [1, 2, 3, 4, -1] : Example after allocating Node #1
+ *    free_list = 2->3->4->-1
+ *
+ *    -- Frees --
+ *    1) Based on the address to be freed, calculate the index of the node
+ *       being freed (cur_idx)
+ *    2) Read the current head (old_head)
+ *    3) So the freed node is going to go at the head of the list, and we
+ *       want to put the old_head after it. So next[cur_idx] = old_head
+ *    4) cmpxchg(head, old_head, cur_idx)
+ *
+ *    head = 0
+ *    next = [2, 2, 3, 4, -1]
+ *    free_list = 0->2->3->4->-1 : Example after freeing Node #0
+ *
+ *    head = 1
+ *    next = [2, 0, 3, 4, -1]
+ *    free_list = 1->0->2->3->4->-1 : Example after freeing Node #1
+ */
+
+#ifndef LOCKLESS_ALLOCATOR_PRIV_H
+#define LOCKLESS_ALLOCATOR_PRIV_H
+
+struct nvgpu_allocator;
+
+struct nvgpu_lockless_allocator {
+        struct nvgpu_allocator *owner;
+
+        u64 base;               /* Base address of the space. */
+        u64 length;             /* Length of the space. */
+        u64 blk_size;           /* Size of the structure being allocated */
+        int nr_nodes;           /* Number of nodes available for allocation */
+
+        int *next;              /* An array holding the next indices per node */
+        int head;               /* Current node at the top of the stack */
+
+        u64 flags;
+
+        bool inited;
+
+        /* Statistics */
+        nvgpu_atomic_t nr_allocs;
+};
+
+static inline struct nvgpu_lockless_allocator *lockless_allocator(
+        struct nvgpu_allocator *a)
+{
+        return (struct nvgpu_lockless_allocator *)(a)->priv;
+}
+
+#endif