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54 lines
2.1 KiB
54 lines
2.1 KiB
/* Copyright 2019 Google LLC. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==============================================================================*/
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#ifndef RUY_RUY_SYSTEM_ALIGNED_ALLOC_H_
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#define RUY_RUY_SYSTEM_ALIGNED_ALLOC_H_
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#include <cstddef>
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namespace ruy {
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namespace detail {
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// Minimum alignment for blocks.
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//
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// Considerations:
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// - This needs to be at least the alignment of any usual data type.
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// - It's useful that this is at least the size of a cache line to limit
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// possible cache side effects (if only on performance behavior).
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// - It's useful that this is at least the size of SIMD registers, as
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// some SIMD instruction sets have at least performance behavior
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// differences (e.g. NEON) or even different requirements (e.g. SSE)
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// based on that.
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// - It's useful that this is at least the size of an "exclusive reservation
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// granule" on ARM, meaning that if we use this Allocator to allocate
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// an atomic variable, there will be no side effects from other things
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// contending for exclusive/atomic memory accesses to it. While the
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// ARM reference manual mentions that this granule size may be as large
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// as 2048 bytes, in practice we observe it to be 64 bytes. It can
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// be queried cheaply, at runtime, from userspace, if needed.
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constexpr std::ptrdiff_t kMinimumBlockAlignment = 64;
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// Primitive allocation functions obtaining aligned memory from the
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// operating system.
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void* SystemAlignedAlloc(std::ptrdiff_t num_bytes);
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void SystemAlignedFree(void* ptr);
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} // namespace detail
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} // namespace ruy
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#endif // RUY_RUY_SYSTEM_ALIGNED_ALLOC_H_
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