1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
|
// Copyright 2015 The Gemmlowp Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// allocator.h: a buffer allocator that allows avoiding most of the
// malloc/free overhead, by:
// 1. Requiring all N allocations to be reserved in advance, and
// then commited at once, turning N allocations into 1.
// 2. Being persistent, the allocated storage is reused across commits,
// and only reallocated as needed when the commit size gets larger.
//
// This is driven by Android-specific needs:
// 1. On Android, the default (Bionic) allocator tends to aggressively
// unmap pages, which means that malloc/free can be surprisingly expensive.
// 2. On Android, stack allocations with alloca() can't be as large as on
// desktop platforms.
//
// General usage:
// 1. Reserve blocks by calling Reserve(), which returns a Handle.
// 2. Call Commit() once.
// 3. Now it is possible to get pointers to allocated buffers by calling
// GetPointer().
// 4. Call Decommit() once.
// 5. The allocator is now reverted to its original state, except that
// it retained its allocated storage, so the next Commit() will be faster.
// The allocated storage is only freed when the Allocator object is
// destroyed.
#ifndef GEMMLOWP_INTERNAL_ALLOCATOR_H_
#define GEMMLOWP_INTERNAL_ALLOCATOR_H_
#include "common.h"
namespace gemmlowp {
enum class TypeId : std::uint8_t { Uint8, Int8, Uint16, Int16, Uint32, Int32 };
template <typename T>
struct GetTypeIdImpl {};
template <typename T>
inline TypeId GetTypeId() {
return GetTypeIdImpl<T>::Value;
}
template <typename T>
struct GetTypeIdImpl<const T> : GetTypeIdImpl<T> {};
#define GEMMLOWP_REGISTER_TYPEID(type_, id) \
template <> \
struct GetTypeIdImpl<type_> { \
static const TypeId Value = TypeId::id; \
};
GEMMLOWP_REGISTER_TYPEID(std::uint8_t, Uint8)
GEMMLOWP_REGISTER_TYPEID(std::int8_t, Int8)
GEMMLOWP_REGISTER_TYPEID(std::uint16_t, Uint16)
GEMMLOWP_REGISTER_TYPEID(std::int16_t, Int16)
GEMMLOWP_REGISTER_TYPEID(std::uint32_t, Uint32)
GEMMLOWP_REGISTER_TYPEID(std::int32_t, Int32)
class Allocator {
public:
Allocator()
: committed_(false),
storage_size_(0),
storage_(nullptr),
reserved_blocks_(0),
reserved_bytes_(0),
generation_(0) {}
~Allocator() {
assert(!committed_);
assert(!reserved_blocks_);
DeallocateStorage();
}
// Alignment of allocated blocks.
static const std::size_t kAlignment = kDefaultCacheLineSize;
// This is all we need so far, and since the usage pattern is fixed,
// there is no point in allowing more until we need to.
static const std::size_t kMaxBlocks = 5;
void Commit() {
assert(!committed_);
if (reserved_bytes_ > storage_size_) {
DeallocateStorage();
storage_size_ = RoundUpToPowerOfTwo(reserved_bytes_);
storage_ = aligned_alloc(kAlignment, storage_size_);
}
ReleaseBuildAssertion(!storage_size_ || storage_, "allocation failure");
committed_ = true;
}
void Decommit() {
assert(committed_);
committed_ = false;
generation_++;
reserved_blocks_ = 0;
reserved_bytes_ = 0;
}
// See generation_
typedef std::size_t generation_t;
// A handle on a reserved block. The user obtains
// one by calling Reserve() and, after committing,
// passes it to GetPointer().
class Handle {
std::uint8_t index_;
generation_t generation_;
TypeId type_;
friend class Allocator;
};
// Reserves a block sized for n elements of type T, and
// returns a handle to it. Must be called before committing.
template <typename T>
Handle Reserve(std::size_t n) {
assert(!committed_ && "can't reserve blocks while committed");
assert(reserved_blocks_ < kMaxBlocks &&
"didn't expect to allocate this many blocks");
const std::size_t bytes = RoundUp<kAlignment>(n * sizeof(T));
const std::size_t offset = reserved_bytes_;
const std::size_t index = reserved_blocks_;
reserved_blocks_offsets_[index] = offset;
Handle h;
h.index_ = index;
h.generation_ = generation_;
h.type_ = GetTypeId<T>();
reserved_blocks_++;
reserved_bytes_ += bytes;
return h;
}
// Returns the pointer to the allocated buffer for the given handle.
// Must be called after committing.
template <typename T>
T* GetPointer(const Handle& h) const {
assert(committed_ && "can't get block pointers unless committed");
assert(h.index_ < reserved_blocks_ &&
"bad handle, points to inexistant block");
assert(h.generation_ == generation_ &&
"handle from earlier generation, have decommitted since");
assert(h.type_ == GetTypeId<T>() && "type mismatch");
std::size_t offset = reserved_blocks_offsets_[h.index_];
std::uintptr_t addr = reinterpret_cast<std::uintptr_t>(storage_) + offset;
return reinterpret_cast<T*>(addr);
}
private:
void DeallocateStorage() {
assert(!committed_);
aligned_free(storage_);
storage_size_ = 0;
}
// Set to true by Commit() and to false by Decommit(). Initially false.
bool committed_;
// The actually allocated storage size and buffer pointer.
std::size_t storage_size_;
mutable void* storage_;
// The number of blocks that have been reserved by Reserve().
std::size_t reserved_blocks_;
// The number of bytes that have been reserved by Reserve().
std::size_t reserved_bytes_;
// The offsets of reserved blocks into the storage buffer.
std::size_t reserved_blocks_offsets_[kMaxBlocks];
// The 'generation' is incremented on Decommit() and allows catching
// bad GetPointer() calls still referring to a previous commit.
generation_t generation_;
};
} // namespace gemmlowp
#endif // GEMMLOWP_INTERNAL_ALLOCATOR_H_
|
