Halide
device_buffer_utils.h
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1 #ifndef HALIDE_RUNTIME_DEVICE_BUFFER_UTILS_H
2 #define HALIDE_RUNTIME_DEVICE_BUFFER_UTILS_H
3 
4 #include "HalideRuntime.h"
5 #include "device_interface.h"
6 #include "printer.h"
7 
8 namespace Halide {
9 namespace Runtime {
10 namespace Internal {
11 
12 // A host <-> dev copy should be done with the fewest possible number
13 // of contiguous copies to minimize driver overhead. If our
14 // halide_buffer_t has strides larger than its extents (e.g. because
15 // it represents a sub-region of a larger halide_buffer_t) we can't
16 // safely copy it back and forth using a single contiguous copy,
17 // because we'd clobber in-between values that another thread might be
18 // using. In the best case we can do a single contiguous copy, but in
19 // the worst case we need to individually copy over every pixel.
20 //
21 // This problem is made extra difficult by the fact that the ordering
22 // of the dimensions in a halide_buffer_t doesn't relate to memory layout at
23 // all, so the strides could be in any order.
24 //
25 // We solve it by representing a copy job we need to perform as a
26 // device_copy struct. It describes a multi-dimensional array of
27 // copies to perform. Initially it describes copying over a single
28 // pixel at a time. We then try to discover contiguous groups of
29 // copies that can be coalesced into a single larger copy.
30 
31 // The struct that describes a host <-> dev copy to perform.
32 #define MAX_COPY_DIMS 16
33 struct device_copy {
34  // opaque handles for source and device memory.
36  // The offset in the source memory to start
38  // The multidimensional array of contiguous copy tasks that need to be done.
40  // The strides (in bytes) that separate adjacent copy tasks in each dimension.
43  // How many contiguous bytes to copy per task
45 };
46 
47 WEAK void copy_memory_helper(const device_copy &copy, int d, int64_t src_off, int64_t dst_off) {
48  // Skip size-1 dimensions
49  while (d >= 0 && copy.extent[d] == 1)
50  d--;
51 
52  if (d == -1) {
53  const void *from = (void *)(copy.src + src_off);
54  void *to = (void *)(copy.dst + dst_off);
55  memcpy(to, from, copy.chunk_size);
56  } else {
57  for (uint64_t i = 0; i < copy.extent[d]; i++) {
58  copy_memory_helper(copy, d - 1, src_off, dst_off);
59  src_off += copy.src_stride_bytes[d];
60  dst_off += copy.dst_stride_bytes[d];
61  }
62  }
63 }
64 
65 WEAK void copy_memory(const device_copy &copy, void *user_context) {
66  // If this is a zero copy buffer, these pointers will be the same.
67  if (copy.src != copy.dst) {
68  copy_memory_helper(copy, MAX_COPY_DIMS - 1, copy.src_begin, 0);
69  } else {
70  debug(user_context) << "copy_memory: no copy needed as pointers are the same.\n";
71  }
72 }
73 
74 // Fills the entire dst buffer, which must be contained within src
76  const halide_buffer_t *dst, bool dst_host) {
77  // Make a copy job representing copying the first pixel only.
78  device_copy c;
79  c.src = src_host ? (uint64_t)src->host : src->device;
80  c.dst = dst_host ? (uint64_t)dst->host : dst->device;
81  c.chunk_size = src->type.bytes();
82  for (int i = 0; i < MAX_COPY_DIMS; i++) {
83  c.extent[i] = 1;
84  c.src_stride_bytes[i] = 0;
85  c.dst_stride_bytes[i] = 0;
86  }
87 
88  // Offset the src base pointer to the right point in its buffer.
89  c.src_begin = 0;
90  for (int i = 0; i < src->dimensions; i++) {
91  c.src_begin += src->dim[i].stride * (dst->dim[i].min - src->dim[i].min);
92  }
93  c.src_begin *= c.chunk_size;
94 
95  if (src->dimensions != dst->dimensions ||
96  src->type.bytes() != dst->type.bytes() ||
97  dst->dimensions > MAX_COPY_DIMS) {
98  // These conditions should also be checked for outside this fn.
99  device_copy zero = {0};
100  return zero;
101  }
102 
103  if (c.chunk_size == 0) {
104  // This buffer apparently represents no memory. Return a zero'd copy
105  // task.
106  device_copy zero = {0};
107  return zero;
108  }
109 
110  // Now expand it to copy all the pixels (one at a time) by taking
111  // the extents and strides from the halide_buffer_ts. Dimensions
112  // are added to the copy by inserting it such that the stride is
113  // in ascending order in the dst.
114  for (int i = 0; i < dst->dimensions; i++) {
115  // TODO: deal with negative strides.
116  uint64_t dst_stride_bytes = dst->dim[i].stride * dst->type.bytes();
117  uint64_t src_stride_bytes = src->dim[i].stride * src->type.bytes();
118  // Insert the dimension sorted into the buffer copy.
119  int insert;
120  for (insert = 0; insert < i; insert++) {
121  // If the stride is 0, we put it at the end because it can't be
122  // folded.
123  if (dst_stride_bytes < c.dst_stride_bytes[insert] && dst_stride_bytes != 0) {
124  break;
125  }
126  }
127  for (int j = i; j > insert; j--) {
128  c.extent[j] = c.extent[j - 1];
129  c.dst_stride_bytes[j] = c.dst_stride_bytes[j - 1];
130  c.src_stride_bytes[j] = c.src_stride_bytes[j - 1];
131  }
132  c.extent[insert] = dst->dim[i].extent;
133  // debug(NULL) << "c.extent[" << insert << "] = " << (int)(c.extent[insert]) << "\n";
134  c.dst_stride_bytes[insert] = dst_stride_bytes;
135  c.src_stride_bytes[insert] = src_stride_bytes;
136  };
137 
138  // Attempt to fold contiguous dimensions into the chunk
139  // size. Since the dimensions are sorted by stride, and the
140  // strides must be greater than or equal to the chunk size, this
141  // means we can just delete the innermost dimension as long as its
142  // stride in both src and dst is equal to the chunk size.
143  while (c.chunk_size == c.src_stride_bytes[0] &&
144  c.chunk_size == c.dst_stride_bytes[0]) {
145  // Fold the innermost dimension's extent into the chunk_size.
146  c.chunk_size *= c.extent[0];
147 
148  // Erase the innermost dimension from the list of dimensions to
149  // iterate over.
150  for (int j = 1; j < MAX_COPY_DIMS; j++) {
151  c.extent[j - 1] = c.extent[j];
152  c.src_stride_bytes[j - 1] = c.src_stride_bytes[j];
153  c.dst_stride_bytes[j - 1] = c.dst_stride_bytes[j];
154  }
155  c.extent[MAX_COPY_DIMS - 1] = 1;
156  c.src_stride_bytes[MAX_COPY_DIMS - 1] = 0;
157  c.dst_stride_bytes[MAX_COPY_DIMS - 1] = 0;
158  }
159  return c;
160 }
161 
163  return make_buffer_copy(buf, true, buf, false);
164 }
165 
167  return make_buffer_copy(buf, false, buf, true);
168 }
169 
170 // Caller is expected to verify that src->dimensions == dst->dimensions
172  int64_t offset = 0;
173  for (int i = 0; i < src->dimensions; i++) {
174  offset += (dst->dim[i].min - src->dim[i].min) * src->dim[i].stride;
175  }
176  offset *= src->type.bytes();
177  return offset;
178 }
179 
180 // Caller is expected to verify that src->dimensions == dst->dimensions + 1,
181 // and that slice_dim and slice_pos are valid within src
182 ALWAYS_INLINE int64_t calc_device_slice_byte_offset(const struct halide_buffer_t *src, int slice_dim, int slice_pos) {
183  int64_t offset = (slice_pos - src->dim[slice_dim].min) * src->dim[slice_dim].stride;
184  offset *= src->type.bytes();
185  return offset;
186 }
187 
188 } // namespace Internal
189 } // namespace Runtime
190 } // namespace Halide
191 
192 #endif // HALIDE_DEVICE_BUFFER_UTILS_H
Halide::Runtime::Internal::make_buffer_copy
WEAK device_copy make_buffer_copy(const halide_buffer_t *src, bool src_host, const halide_buffer_t *dst, bool dst_host)
Definition: device_buffer_utils.h:75
Halide::Runtime::Internal::device_copy
Definition: device_buffer_utils.h:33
Halide::Runtime::Internal::copy_memory
WEAK void copy_memory(const device_copy &copy, void *user_context)
Definition: device_buffer_utils.h:65
device_interface.h
halide_buffer_t::dim
halide_dimension_t * dim
The shape of the buffer.
Definition: HalideRuntime.h:1427
Halide::Runtime::Internal::device_copy::dst_stride_bytes
uint64_t dst_stride_bytes[MAX_COPY_DIMS]
Definition: device_buffer_utils.h:42
Halide::Runtime::Internal::device_copy::src_stride_bytes
uint64_t src_stride_bytes[MAX_COPY_DIMS]
Definition: device_buffer_utils.h:41
halide_buffer_t::type
struct halide_type_t type
The type of each buffer element.
Definition: HalideRuntime.h:1420
uint64_t
unsigned __INT64_TYPE__ uint64_t
Definition: runtime_internal.h:19
Halide::Runtime::Internal::device_copy::extent
uint64_t extent[MAX_COPY_DIMS]
Definition: device_buffer_utils.h:39
Halide
This file defines the class FunctionDAG, which is our representation of a Halide pipeline,...
Definition: AddAtomicMutex.h:21
halide_buffer_t::dimensions
int32_t dimensions
The dimensionality of the buffer.
Definition: HalideRuntime.h:1423
Halide::LinkageType::Internal
@ Internal
Not visible externally, similar to 'static' linkage in C.
Halide::Runtime::Internal::device_copy::chunk_size
uint64_t chunk_size
Definition: device_buffer_utils.h:44
MAX_COPY_DIMS
#define MAX_COPY_DIMS
Definition: device_buffer_utils.h:32
printer.h
Halide::Runtime::Internal::copy_memory_helper
WEAK void copy_memory_helper(const device_copy &copy, int d, int64_t src_off, int64_t dst_off)
Definition: device_buffer_utils.h:47
int64_t
signed __INT64_TYPE__ int64_t
Definition: runtime_internal.h:18
Halide::Runtime::Internal::calc_device_slice_byte_offset
ALWAYS_INLINE int64_t calc_device_slice_byte_offset(const struct halide_buffer_t *src, int slice_dim, int slice_pos)
Definition: device_buffer_utils.h:182
halide_buffer_t::host
uint8_t * host
A pointer to the start of the data in main memory.
Definition: HalideRuntime.h:1414
Halide::Runtime::Internal::make_device_to_host_copy
WEAK device_copy make_device_to_host_copy(const halide_buffer_t *buf)
Definition: device_buffer_utils.h:166
Halide::Runtime::Internal::device_copy::dst
uint64_t dst
Definition: device_buffer_utils.h:35
Halide::Runtime::Internal::make_host_to_device_copy
WEAK device_copy make_host_to_device_copy(const halide_buffer_t *buf)
Definition: device_buffer_utils.h:162
ALWAYS_INLINE
#define ALWAYS_INLINE
Definition: runtime_internal.h:53
dst
char * dst
Definition: printer.h:32
HalideRuntime.h
memcpy
void * memcpy(void *s1, const void *s2, size_t n)
halide_buffer_t
The raw representation of an image passed around by generated Halide code.
Definition: HalideRuntime.h:1404
halide_dimension_t::stride
int32_t stride
Definition: HalideRuntime.h:1366
buf
char * buf
Definition: printer.h:32
Halide::Runtime::Internal::device_copy::src
uint64_t src
Definition: device_buffer_utils.h:35
Halide::Runtime::Internal::calc_device_crop_byte_offset
ALWAYS_INLINE int64_t calc_device_crop_byte_offset(const struct halide_buffer_t *src, struct halide_buffer_t *dst)
Definition: device_buffer_utils.h:171
WEAK
#define WEAK
Definition: runtime_internal.h:50
Halide::Runtime::Internal::device_copy::src_begin
uint64_t src_begin
Definition: device_buffer_utils.h:37
halide_dimension_t::min
int32_t min
Definition: HalideRuntime.h:1366
user_context
void * user_context
Definition: printer.h:33
halide_buffer_t::device
uint64_t device
A device-handle for e.g.
Definition: HalideRuntime.h:1406