-- 3d018c03a34bf273a4b24b3584ed77f0a6d21686 by Abseil Team <absl-team@google.com>: Fix a spelling typo (s/boundries/boundaries). PiperOrigin-RevId: 442041877 Change-Id: I608020697d37b85316bb9a0838e4b457659c926c -- 518b8119e51db24ce7fb0fd2fe537ec43825c3e6 by Dino Radakovic <dinor@google.com>: absl/types/internal/variant: Make include guard uppercase https://google.github.io/styleguide/cppguide.html#The__define_Guard PiperOrigin-RevId: 441911692 Change-Id: I9837dd07f20204d8253f20627b0917a34dc21825 -- b91696c38310a7cae8c1ea9e2d479495f5dc3f69 by Greg Falcon <gfalcon@google.com>: Add an internal-only API to wrap __builtin_prefetch() if available. This private API is intended for future use by the Abseil implementation. Like any internal-namespaced function, it may be changed or removed at any time. PiperOrigin-RevId: 441894616 Change-Id: Iaa48bd4680b373f4a0d5afab0cb35e2a1908595f -- 0f01e8b0551a662e02dff60840c54320f987315f by Derek Mauro <dmauro@google.com>: C++20: Use the standard `constinit` keyword for `ABSL_CONST_INIT` when available PiperOrigin-RevId: 441778874 Change-Id: I70c616469752ff23b326b1c615437599f42cc6aa GitOrigin-RevId: 3d018c03a34bf273a4b24b3584ed77f0a6d21686pull/1157/head
Abseil Team
3 years ago
committed by
Andy Getz
parent
8c6e53ef3a
commit
c27ab06897
15 changed files with 245 additions and 24 deletions
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// Copyright 2022 The Abseil Authors.
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//
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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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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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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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#ifndef ABSL_BASE_INTERNAL_PREFETCH_H_ |
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#define ABSL_BASE_INTERNAL_PREFETCH_H_ |
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#include "absl/base/config.h" |
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// Compatibility wrappers around __builtin_prefetch, to prefetch data
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// for read if supported by the toolchain.
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// Move data into the cache before it is read, or "prefetch" it.
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//
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// The value of `addr` is the address of the memory to prefetch. If
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// the target and compiler support it, data prefetch instructions are
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// generated. If the prefetch is done some time before the memory is
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// read, it may be in the cache by the time the read occurs.
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//
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// The function names specify the temporal locality heuristic applied,
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// using the names of Intel prefetch instructions:
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//
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// T0 - high degree of temporal locality; data should be left in as
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// many levels of the cache possible
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// T1 - moderate degree of temporal locality
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// T2 - low degree of temporal locality
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// Nta - no temporal locality, data need not be left in the cache
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// after the read
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//
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// Incorrect or gratuitous use of these functions can degrade
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// performance, so use them only when representative benchmarks show
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// an improvement.
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//
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// Example usage:
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//
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// absl::base_internal::PrefetchT0(addr);
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//
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// Currently, the different prefetch calls behave on some Intel
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// architectures as follows:
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//
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// SNB..SKL SKX
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// PrefetchT0() L1/L2/L3 L1/L2
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// PrefetchT1() L2/L3 L2
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// PrefetchT2() L2/L3 L2
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// PrefetchNta() L1/--/L3 L1*
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//
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// * On SKX PrefetchNta() will bring the line into L1 but will evict
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// from L3 cache. This might result in surprising behavior.
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//
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// SNB = Sandy Bridge, SKL = Skylake, SKX = Skylake Xeon.
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//
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace base_internal { |
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void PrefetchT0(const void* addr); |
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void PrefetchT1(const void* addr); |
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void PrefetchT2(const void* addr); |
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void PrefetchNta(const void* addr); |
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// Implementation details follow.
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#if ABSL_HAVE_BUILTIN(__builtin_prefetch) || defined(__GNUC__) |
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// See __builtin_prefetch:
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// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html.
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//
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// These functions speculatively load for read only. This is
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// safe for all currently supported platforms. However, prefetch for
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// store may have problems depending on the target platform.
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//
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inline void PrefetchT0(const void* addr) { |
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// Note: this uses prefetcht0 on Intel.
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__builtin_prefetch(addr, 0, 3); |
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} |
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inline void PrefetchT1(const void* addr) { |
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// Note: this uses prefetcht1 on Intel.
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__builtin_prefetch(addr, 0, 2); |
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} |
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inline void PrefetchT2(const void* addr) { |
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// Note: this uses prefetcht2 on Intel.
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__builtin_prefetch(addr, 0, 1); |
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} |
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inline void PrefetchNta(const void* addr) { |
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// Note: this uses prefetchtnta on Intel.
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__builtin_prefetch(addr, 0, 0); |
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} |
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#else |
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inline void PrefetchT0(const void*) {} |
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inline void PrefetchT1(const void*) {} |
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inline void PrefetchT2(const void*) {} |
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inline void PrefetchNta(const void*) {} |
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#endif |
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} // namespace base_internal
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ABSL_NAMESPACE_END |
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} // namespace absl
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#endif // ABSL_BASE_INTERNAL_PREFETCH_H_
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// Copyright 2022 The Abseil Authors.
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//
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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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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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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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#include "absl/base/internal/prefetch.h" |
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#include "gtest/gtest.h" |
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namespace { |
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int number = 42; |
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TEST(Prefetch, TemporalLocalityNone) { |
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absl::base_internal::PrefetchNta(&number); |
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EXPECT_EQ(number, 42); |
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} |
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TEST(Prefetch, TemporalLocalityLow) { |
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absl::base_internal::PrefetchT2(&number); |
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EXPECT_EQ(number, 42); |
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} |
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TEST(Prefetch, TemporalLocalityMedium) { |
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absl::base_internal::PrefetchT1(&number); |
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EXPECT_EQ(number, 42); |
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} |
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TEST(Prefetch, TemporalLocalityHigh) { |
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absl::base_internal::PrefetchT0(&number); |
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EXPECT_EQ(number, 42); |
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} |
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} // namespace
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