yield-processor.h

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// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef V8_BASE_PLATFORM_YIELD_PROCESSOR_H_
#define V8_BASE_PLATFORM_YIELD_PROCESSOR_H_
 
// The YIELD_PROCESSOR macro wraps an architecture specific-instruction that
// informs the processor we're in a busy wait, so it can handle the branch more
// intelligently and e.g. reduce power to our core or give more resources to the
// other hyper-thread on this core. See the following for context:
// https://software.intel.com/en-us/articles/benefitting-power-and-performance-sleep-loops
 
#if defined(THREAD_SANITIZER)
#include "src/base/platform/platform.h"
// TSAN intercepts atomic accesses and uses locking. Since YIELD_PROCESSOR is
// used in spinlock loops in conjunction with atomic accesses, such spinlock
// loops can exhibit starvation in TSAN. To work around the problem, have
// YIELD_PROCESSOR sleep the process for 1ms.
#define YIELD_PROCESSOR base::OS::Sleep(base::TimeDelta::FromMilliseconds(1))
 
#else  // !THREAD_SANITIZER
 
#if defined(V8_CC_MSVC)
// MSVC does not support inline assembly via __asm__ and provides compiler
// intrinsics instead. Check if there is a usable intrinsic.
//
// intrin.h is an expensive header, so only include it if we're on a host
// architecture that has a usable intrinsic.
#if defined(V8_HOST_ARCH_IA32) || defined(V8_HOST_ARCH_X64)
#include <intrin.h>
#define YIELD_PROCESSOR _mm_pause()
#elif defined(V8_HOST_ARCH_ARM64) || \
    (defined(V8_HOST_ARCH_ARM) && __ARM_ARCH >= 6)
#include <intrin.h>
#define YIELD_PROCESSOR __yield()
#endif  // V8_HOST_ARCH
 
#else  // !V8_CC_MSVC
 
#if defined(V8_HOST_ARCH_IA32) || defined(V8_HOST_ARCH_X64)
#define YIELD_PROCESSOR __asm__ __volatile__("pause")
#elif defined(V8_HOST_ARCH_ARM64) || \
    (defined(V8_HOST_ARCH_ARM) && __ARM_ARCH >= 6)
#define YIELD_PROCESSOR __asm__ __volatile__("yield")
#elif defined(V8_HOST_ARCH_MIPS64EL) && __mips_isa_rev >= 2
// Don't bother doing using .word here since r2 is the lowest supported mips64
// that Chromium supports.
#define YIELD_PROCESSOR __asm__ __volatile__("pause")
#elif defined(V8_HOST_ARCH_PPC64)
#define YIELD_PROCESSOR __asm__ __volatile__("or 31,31,31")
#endif  // V8_HOST_ARCH
 
#endif  // V8_CC_MSVC
 
#endif  // THREAD_SANITIZER
 
#ifndef YIELD_PROCESSOR
#define YIELD_PROCESSOR ((void)0)
#endif
 
#endif  // V8_BASE_PLATFORM_YIELD_PROCESSOR_H_