gpu: nvgpu: implement lockless allocator

Implement a lockless allocator for fixed-size data
structures.

Bug 1795076

Change-Id: I70a5f52cbdb4452cc0fd9a8edf26735be29ede57
Signed-off-by: Sachit Kadle <skadle@nvidia.com>
Reviewed-on: http://git-master/r/1213211
(cherry picked from commit e4bff7da0f39c8f4b5691169c02e482bc9d4166e)
Reviewed-on: http://git-master/r/1223246
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>

4 files changed, 335 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/Makefile.nvgpu b/drivers/gpu/nvgpu/Makefile.nvgpu
index b8e38919..33d158bb 100644
--- a/drivers/gpu/nvgpu/Makefile.nvgpu
+++ b/drivers/gpu/nvgpu/Makefile.nvgpu
@@ -57,6 +57,7 @@ nvgpu-y := \
         gk20a/gk20a_allocator_bitmap.o \
         gk20a/gk20a_allocator_buddy.o \
         gk20a/gk20a_allocator_page.o \
+        gk20a/gk20a_allocator_lockless.o \
         gk20a/cde_gk20a.o \
         gk20a/platform_gk20a_generic.o \
         gk20a/tsg_gk20a.o \
diff --git a/drivers/gpu/nvgpu/gk20a/gk20a_allocator.h b/drivers/gpu/nvgpu/gk20a/gk20a_allocator.h
index 93865190..0d611ba3 100644
--- a/drivers/gpu/nvgpu/gk20a/gk20a_allocator.h
+++ b/drivers/gpu/nvgpu/gk20a/gk20a_allocator.h
@@ -165,6 +165,15 @@ int gk20a_page_allocator_init(struct gk20a_allocator *__a,
                               const char *name, u64 base, u64 length,
                               u64 blk_size, u64 flags);
 
+/*
+ * Lockless allocatior initializers.
+ * Note: This allocator can only allocate fixed-size structures of a
+ * pre-defined size.
+ */
+int gk20a_lockless_allocator_init(struct gk20a_allocator *__a,
+                                  const char *name, u64 base, u64 length,
+                                  u64 struct_size, u64 flags);
+
 #define GPU_BALLOC_MAX_ORDER            31
 
 /*
diff --git a/drivers/gpu/nvgpu/gk20a/gk20a_allocator_lockless.c b/drivers/gpu/nvgpu/gk20a/gk20a_allocator_lockless.c
new file mode 100644
index 00000000..32455c98
--- /dev/null
+++ b/drivers/gpu/nvgpu/gk20a/gk20a_allocator_lockless.c
@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2016, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+
+#include "gk20a_allocator.h"
+#include "lockless_allocator_priv.h"
+
+static u64 gk20a_lockless_alloc_length(struct gk20a_allocator *a)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+
+        return pa->length;
+}
+
+static u64 gk20a_lockless_alloc_base(struct gk20a_allocator *a)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+
+        return pa->base;
+}
+
+static int gk20a_lockless_alloc_inited(struct gk20a_allocator *a)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+        int inited = pa->inited;
+
+        rmb();
+        return inited;
+}
+
+static u64 gk20a_lockless_alloc_end(struct gk20a_allocator *a)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+
+        return pa->base + pa->length;
+}
+
+static u64 gk20a_lockless_alloc(struct gk20a_allocator *a, u64 len)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+        int head, new_head, ret;
+        u64 addr = 0;
+
+        if (len != pa->blk_size)
+                return 0;
+
+        head = ACCESS_ONCE(pa->head);
+        while (head >= 0) {
+                new_head = ACCESS_ONCE(pa->next[head]);
+                ret = cmpxchg(&pa->head, head, new_head);
+                if (ret == head) {
+                        addr = pa->base + head * pa->blk_size;
+                        atomic_inc(&pa->nr_allocs);
+                        alloc_dbg(a, "Alloc node # %d @ addr 0x%llx\n", head,
+                                  addr);
+                        break;
+                }
+                head = ACCESS_ONCE(pa->head);
+        }
+        return addr;
+}
+
+static void gk20a_lockless_free(struct gk20a_allocator *a, u64 addr)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+        int head, ret;
+        u64 cur_idx, rem;
+
+        cur_idx = addr - pa->base;
+        rem = do_div(cur_idx, pa->blk_size);
+
+        while (1) {
+                head = ACCESS_ONCE(pa->head);
+                ACCESS_ONCE(pa->next[cur_idx]) = head;
+                ret = cmpxchg(&pa->head, head, cur_idx);
+                if (ret == head) {
+                        atomic_dec(&pa->nr_allocs);
+                        alloc_dbg(a, "Free node # %llu\n", cur_idx);
+                        break;
+                }
+        }
+}
+
+static void gk20a_lockless_alloc_destroy(struct gk20a_allocator *a)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+
+        vfree(pa->next);
+        kfree(pa);
+}
+
+static void gk20a_lockless_print_stats(struct gk20a_allocator *a,
+                                   struct seq_file *s, int lock)
+{
+        struct gk20a_lockless_allocator *pa = a->priv;
+
+        __alloc_pstat(s, a, "Lockless allocator params:\n");
+        __alloc_pstat(s, a, "  start = 0x%llx\n", pa->base);
+        __alloc_pstat(s, a, "  end   = 0x%llx\n", pa->base + pa->length);
+
+        /* Actual stats. */
+        __alloc_pstat(s, a, "Stats:\n");
+        __alloc_pstat(s, a, "  Number allocs = %d\n",
+                      atomic_read(&pa->nr_allocs));
+        __alloc_pstat(s, a, "  Number free   = %d\n",
+                      pa->nr_nodes - atomic_read(&pa->nr_allocs));
+}
+
+static const struct gk20a_allocator_ops pool_ops = {
+        .alloc          = gk20a_lockless_alloc,
+        .free           = gk20a_lockless_free,
+
+        .base           = gk20a_lockless_alloc_base,
+        .length         = gk20a_lockless_alloc_length,
+        .end            = gk20a_lockless_alloc_end,
+        .inited         = gk20a_lockless_alloc_inited,
+
+        .fini           = gk20a_lockless_alloc_destroy,
+
+        .print_stats    = gk20a_lockless_print_stats,
+};
+
+int gk20a_lockless_allocator_init(struct gk20a_allocator *__a,
+                              const char *name, u64 base, u64 length,
+                              u64 blk_size, u64 flags)
+{
+        int i;
+        int err;
+        int nr_nodes;
+        u64 count, rem;
+        struct gk20a_lockless_allocator *a;
+
+        if (!blk_size)
+                return -EINVAL;
+
+        /*
+         * Ensure we have space for atleast one node & there's no overflow.
+         * In order to control memory footprint, we require count < INT_MAX
+         */
+        count = length;
+        rem = do_div(count, blk_size);
+        if (!base || !count || count > INT_MAX)
+                return -EINVAL;
+
+        a = kzalloc(sizeof(struct gk20a_lockless_allocator), GFP_KERNEL);
+        if (!a)
+                return -ENOMEM;
+
+        err = __gk20a_alloc_common_init(__a, name, a, false, &pool_ops);
+        if (err)
+                goto fail;
+
+        a->next = vzalloc(sizeof(*a->next) * count);
+        if (!a->next) {
+                err = -ENOMEM;
+                goto fail;
+        }
+
+        /* chain the elements together to form the initial free list  */
+        nr_nodes = (int)count;
+        for (i = 0; i < nr_nodes; i++)
+                a->next[i] = i + 1;
+        a->next[nr_nodes - 1] = -1;
+
+        a->base = base;
+        a->length = length;
+        a->blk_size = blk_size;
+        a->nr_nodes = nr_nodes;
+        a->flags = flags;
+        atomic_set(&a->nr_allocs, 0);
+
+        wmb();
+        a->inited = true;
+
+        gk20a_init_alloc_debug(__a);
+        alloc_dbg(__a, "New allocator: type          lockless\n");
+        alloc_dbg(__a, "               base          0x%llx\n", a->base);
+        alloc_dbg(__a, "               nodes         %d\n", a->nr_nodes);
+        alloc_dbg(__a, "               blk_size      0x%llx\n", a->blk_size);
+        alloc_dbg(__a, "               flags         0x%llx\n", a->flags);
+
+        return 0;
+
+fail:
+        kfree(a);
+        return err;
+}
diff --git a/drivers/gpu/nvgpu/gk20a/lockless_allocator_priv.h b/drivers/gpu/nvgpu/gk20a/lockless_allocator_priv.h
new file mode 100644
index 00000000..f9b03e0e
--- /dev/null
+++ b/drivers/gpu/nvgpu/gk20a/lockless_allocator_priv.h
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2016, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * 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 gk20a_allocator;
+
+struct gk20a_lockless_allocator {
+        struct gk20a_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 */
+        atomic_t nr_allocs;
+};
+
+static inline struct gk20a_lockless_allocator *lockless_allocator(
+        struct gk20a_allocator *a)
+{
+        return (struct gk20a_lockless_allocator *)(a)->priv;
+}
+
+#endif