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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <cstdint>
namespace folly {
// Memory locations within the same cache line are subject to destructive
// interference, also known as false sharing, which is when concurrent
// accesses to these different memory locations from different cores, where at
// least one of the concurrent accesses is or involves a store operation,
// induce contention and harm performance.
//
// Microbenchmarks indicate that pairs of cache lines also see destructive
// interference under heavy use of atomic operations, as observed for atomic
// increment on Sandy Bridge.
//
// We assume a cache line size of 64, so we use a cache line pair size of 128
// to avoid destructive interference.
//
// mimic: std::hardware_destructive_interference_size, C++17
constexpr std::size_t hardware_destructive_interference_size = 128;
// Memory locations within the same cache line are subject to constructive
// interference, also known as true sharing, which is when accesses to some
// memory locations induce all memory locations within the same cache line to
// be cached, benefiting subsequent accesses to different memory locations
// within the same cache line and heping performance.
//
// mimic: std::hardware_constructive_interference_size, C++17
constexpr std::size_t hardware_constructive_interference_size = 64;
} // namespace folly
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