diff options
Diffstat (limited to 'abseil-cpp/absl/base/internal/prefetch.h')
| -rw-r--r-- | abseil-cpp/absl/base/internal/prefetch.h | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/abseil-cpp/absl/base/internal/prefetch.h b/abseil-cpp/absl/base/internal/prefetch.h new file mode 100644 index 0000000..aecfd87 --- /dev/null +++ b/abseil-cpp/absl/base/internal/prefetch.h @@ -0,0 +1,137 @@ +// Copyright 2022 The Abseil Authors. +// +// 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 +// +// https://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. + +// TODO(b/265984188): remove all uses and delete this header. + +#ifndef ABSL_BASE_INTERNAL_PREFETCH_H_ +#define ABSL_BASE_INTERNAL_PREFETCH_H_ + +#include "absl/base/attributes.h" +#include "absl/base/config.h" +#include "absl/base/prefetch.h" + +#ifdef __SSE__ +#include <xmmintrin.h> +#endif + +#if defined(_MSC_VER) && defined(ABSL_INTERNAL_HAVE_SSE) +#include <intrin.h> +#pragma intrinsic(_mm_prefetch) +#endif + +// Compatibility wrappers around __builtin_prefetch, to prefetch data +// for read if supported by the toolchain. + +// Move data into the cache before it is read, or "prefetch" it. +// +// The value of `addr` is the address of the memory to prefetch. If +// the target and compiler support it, data prefetch instructions are +// generated. If the prefetch is done some time before the memory is +// read, it may be in the cache by the time the read occurs. +// +// The function names specify the temporal locality heuristic applied, +// using the names of Intel prefetch instructions: +// +// T0 - high degree of temporal locality; data should be left in as +// many levels of the cache possible +// T1 - moderate degree of temporal locality +// T2 - low degree of temporal locality +// Nta - no temporal locality, data need not be left in the cache +// after the read +// +// Incorrect or gratuitous use of these functions can degrade +// performance, so use them only when representative benchmarks show +// an improvement. +// +// Example usage: +// +// absl::base_internal::PrefetchT0(addr); +// +// Currently, the different prefetch calls behave on some Intel +// architectures as follows: +// +// SNB..SKL SKX +// PrefetchT0() L1/L2/L3 L1/L2 +// PrefetchT1() L2/L3 L2 +// PrefetchT2() L2/L3 L2 +// PrefetchNta() L1/--/L3 L1* +// +// * On SKX PrefetchNta() will bring the line into L1 but will evict +// from L3 cache. This might result in surprising behavior. +// +// SNB = Sandy Bridge, SKL = Skylake, SKX = Skylake Xeon. +// +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace base_internal { + +ABSL_DEPRECATED("Use absl::PrefetchToLocalCache() instead") +inline void PrefetchT0(const void* address) { + absl::PrefetchToLocalCache(address); +} + +ABSL_DEPRECATED("Use absl::PrefetchToLocalCache() instead") +inline void PrefetchNta(const void* address) { + absl::PrefetchToLocalCacheNta(address); +} + +ABSL_DEPRECATED("Use __builtin_prefetch() for advanced prefetch logic instead") +void PrefetchT1(const void* addr); + +ABSL_DEPRECATED("Use __builtin_prefetch() for advanced prefetch logic instead") +void PrefetchT2(const void* addr); + +// Implementation details follow. + +#if ABSL_HAVE_BUILTIN(__builtin_prefetch) || defined(__GNUC__) + +#define ABSL_INTERNAL_HAVE_PREFETCH 1 + +// See __builtin_prefetch: +// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html. +// +// These functions speculatively load for read only. This is +// safe for all currently supported platforms. However, prefetch for +// store may have problems depending on the target platform. +// +inline void PrefetchT1(const void* addr) { + // Note: this uses prefetcht1 on Intel. + __builtin_prefetch(addr, 0, 2); +} +inline void PrefetchT2(const void* addr) { + // Note: this uses prefetcht2 on Intel. + __builtin_prefetch(addr, 0, 1); +} + +#elif defined(ABSL_INTERNAL_HAVE_SSE) + +#define ABSL_INTERNAL_HAVE_PREFETCH 1 + +inline void PrefetchT1(const void* addr) { + _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T1); +} +inline void PrefetchT2(const void* addr) { + _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T2); +} + +#else +inline void PrefetchT1(const void*) {} +inline void PrefetchT2(const void*) {} +#endif + +} // namespace base_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_BASE_INTERNAL_PREFETCH_H_ |