跟Google学写代码--Chromium/base--cpu源码学习及应用

心已赠人 2022-07-14 14:14 109阅读 0赞

Chromium是一个伟大的、庞大的开源工程，很多值得我们学习的地方。  
前面写道：  
《[跟Google学写代码–Chromium/base–stl\_util源码学习及应用][Google_Chromium_base_stl_util]》

《[跟Google学写代码–Chromium/base–windows\_version源码学习及应用][Google_Chromium_base_windows_version]》

今天分享cpu相关的操作。

先看看这个枚举：

enum IntelMicroArchitecture {
        PENTIUM,
        SSE,
        SSE2,
        SSE3,
        SSSE3,
        SSE41,
        SSE42,
        AVX,
        MAX_INTEL_MICRO_ARCHITECTURE
      };

**什么是sse?**  
SSE(Streaming SIMD Extensions)是英特尔在AMD的3D Now!发布一年之后，在其计算机芯片Pentium III中引入的指令集，是MMX的超集。

SSE2  
SSE2是Intel在Pentium 4处理器的最初版本中引入的，但是AMD后来在Opteron 和Athlon 64处理器中也加入了SSE2的支持。SSE2指令集添加了对64位双精度浮点数的支持。这个指令集还增加了对CPU快取的控制指令。AMD对它的扩展增加了8个XMM寄存器，但是需要切换到64位模式（AMD64）才可以使用这些寄存器。

SSE3  
SSE3是Intel在Pentium 4处理器的 Prescott 核心中引入的第三代SIMD指令集，AMD在Athlon 64的第五个版本，Venice核心中也加入了SSE3的支持。以及对超执行绪技术的支持。  
SSSE3  
SSSE3是Intel针对SSE3指令集的一次额外扩充，最早内建于Core 2 Duo处理器中。

SSE4  
SSE4是Intel在Penryn核心的Core 2 Duo与Core 2 Solo处理器时，新增的47条新多媒体指令集，多媒体指令集，并内建在Phenom与Opteron等K10架构处理器中，不过无法与Intel的SSE4系列指令集相容。

SSE5  
SSE5\]是AMD为了打破Intel垄断在处理器指令集的独霸地位所提出的，SSE5初期规划将加入超过100条新指令，其中最引人注目的就是三算子指令（3-Operand Instructions）及熔合乘法累积（Fused Multiply Accumulate）。其中，三算子指令让处理器可将一个数学或逻辑函式库，套用到算子或输入资料。借由增加算子的数量，一个 x86 指令能处理二至三笔资料， SSE5 允许将多个简单指令汇整成一个指令，达到更有效率的指令处理模式。提升为三运算指令的运算能力，是少数 RISC 架构的水平。熔合乘法累积让允许建立新的指令，有效率地执行各种复杂的运算。熔合乘法累积可结合乘法与加法运算，透过单一指令执行多笔重复计算。透过简化程式码，让系统能迅速执行绘图着色、快速相片着色、音场音效，以及复杂向量演算等效能密集的应用作业。SSE5最快将内建于AMD下一代Bulldozer核心。

AVX  
AVX是Intel的SSE延伸架构，如IA16至IA32般的把暂存器XMM 128bit提升至YMM 256bit，以增加一倍的运算效率。此架构支持了三运算指令（3-Operand Instructions），减少在编码上需要先复制才能运算的动作。在微码部分使用了LES LDS这两少用的指令作为延伸指令Prefix。

**cpu.h**  
由于这个类比较简短，所以就贴上所有的头文件了：

#ifndef BASE_CPU_H_
    #define BASE_CPU_H_
    
    #include <string>
    
    #include "base/base_export.h"
    
    namespace base {
    
    // Query information about the processor.
    class BASE_EXPORT CPU {
     public:
      // Constructor
      CPU();
    
      enum IntelMicroArchitecture {
        PENTIUM,
        SSE,
        SSE2,
        SSE3,
        SSSE3,
        SSE41,
        SSE42,
        AVX,
        MAX_INTEL_MICRO_ARCHITECTURE
      };
    
      // Accessors for CPU information.
      const std::string& vendor_name() const { return cpu_vendor_; }
      int signature() const { return signature_; }
      int stepping() const { return stepping_; }
      int model() const { return model_; }
      int family() const { return family_; }
      int type() const { return type_; }
      int extended_model() const { return ext_model_; }
      int extended_family() const { return ext_family_; }
      bool has_mmx() const { return has_mmx_; }
      bool has_sse() const { return has_sse_; }
      bool has_sse2() const { return has_sse2_; }
      bool has_sse3() const { return has_sse3_; }
      bool has_ssse3() const { return has_ssse3_; }
      bool has_sse41() const { return has_sse41_; }
      bool has_sse42() const { return has_sse42_; }
      bool has_avx() const { return has_avx_; }
      // has_avx_hardware returns true when AVX is present in the CPU. This might
      // differ from the value of |has_avx()| because |has_avx()| also tests for
      // operating system support needed to actually call AVX instuctions.
      // Note: you should never need to call this function. It was added in order
      // to workaround a bug in NSS but |has_avx()| is what you want.
      bool has_avx_hardware() const { return has_avx_hardware_; }
      bool has_aesni() const { return has_aesni_; }
      bool has_non_stop_time_stamp_counter() const {
        return has_non_stop_time_stamp_counter_;
      }
      // has_broken_neon is only valid on ARM chips. If true, it indicates that we
      // believe that the NEON unit on the current CPU is flawed and cannot execute
      // some code. See https://code.google.com/p/chromium/issues/detail?id=341598
      bool has_broken_neon() const { return has_broken_neon_; }
    
      IntelMicroArchitecture GetIntelMicroArchitecture() const;
      const std::string& cpu_brand() const { return cpu_brand_; }
    
     private:
      // Query the processor for CPUID information.
      void Initialize();
    
      int signature_;  // raw form of type, family, model, and stepping
      int type_;  // process type
      int family_;  // family of the processor
      int model_;  // model of processor
      int stepping_;  // processor revision number
      int ext_model_;
      int ext_family_;
      bool has_mmx_;
      bool has_sse_;
      bool has_sse2_;
      bool has_sse3_;
      bool has_ssse3_;
      bool has_sse41_;
      bool has_sse42_;
      bool has_avx_;
      bool has_avx_hardware_;
      bool has_aesni_;
      bool has_non_stop_time_stamp_counter_;
      bool has_broken_neon_;
      std::string cpu_vendor_;
      std::string cpu_brand_;
    };
    
    }  // namespace base
    
    #endif // BASE_CPU_H_

**Initialize的实现**

void CPU::Initialize() {
    #if defined(ARCH_CPU_X86_FAMILY)
      int cpu_info[4] = {-1};
      char cpu_string[48];
    
      // __cpuid with an InfoType argument of 0 returns the number of
      // valid Ids in CPUInfo[0] and the CPU identification string in
      // the other three array elements. The CPU identification string is
      // not in linear order. The code below arranges the information
      // in a human readable form. The human readable order is CPUInfo[1] |
      // CPUInfo[3] | CPUInfo[2]. CPUInfo[2] and CPUInfo[3] are swapped
      // before using memcpy to copy these three array elements to cpu_string.
      __cpuid(cpu_info, 0);
      int num_ids = cpu_info[0];
      std::swap(cpu_info[2], cpu_info[3]);
      memcpy(cpu_string, &cpu_info[1], 3 * sizeof(cpu_info[1]));
      cpu_vendor_.assign(cpu_string, 3 * sizeof(cpu_info[1]));
    
      // Interpret CPU feature information.
      if (num_ids > 0) {
        __cpuid(cpu_info, 1);
        signature_ = cpu_info[0];
        stepping_ = cpu_info[0] & 0xf;
        model_ = ((cpu_info[0] >> 4) & 0xf) + ((cpu_info[0] >> 12) & 0xf0);
        family_ = (cpu_info[0] >> 8) & 0xf;
        type_ = (cpu_info[0] >> 12) & 0x3;
        ext_model_ = (cpu_info[0] >> 16) & 0xf;
        ext_family_ = (cpu_info[0] >> 20) & 0xff;
        has_mmx_ =   (cpu_info[3] & 0x00800000) != 0;
        has_sse_ =   (cpu_info[3] & 0x02000000) != 0;
        has_sse2_ =  (cpu_info[3] & 0x04000000) != 0;
        has_sse3_ =  (cpu_info[2] & 0x00000001) != 0;
        has_ssse3_ = (cpu_info[2] & 0x00000200) != 0;
        has_sse41_ = (cpu_info[2] & 0x00080000) != 0;
        has_sse42_ = (cpu_info[2] & 0x00100000) != 0;
        has_avx_hardware_ =
                     (cpu_info[2] & 0x10000000) != 0;
        // AVX instructions will generate an illegal instruction exception unless
        // a) they are supported by the CPU,
        // b) XSAVE is supported by the CPU and
        // c) XSAVE is enabled by the kernel.
        // See http://software.intel.com/en-us/blogs/2011/04/14/is-avx-enabled
        //
        // In addition, we have observed some crashes with the xgetbv instruction
        // even after following Intel's example code. (See crbug.com/375968.)
        // Because of that, we also test the XSAVE bit because its description in
        // the CPUID documentation suggests that it signals xgetbv support.
        has_avx_ =
            has_avx_hardware_ &&
            (cpu_info[2] & 0x04000000) != 0 /* XSAVE */ &&
            (cpu_info[2] & 0x08000000) != 0 /* OSXSAVE */ &&
            (_xgetbv(0) & 6) == 6 /* XSAVE enabled by kernel */;
        has_aesni_ = (cpu_info[2] & 0x02000000) != 0;
      }
    
      // Get the brand string of the cpu.
      __cpuid(cpu_info, 0x80000000);
      const int parameter_end = 0x80000004;
      int max_parameter = cpu_info[0];
    
      if (cpu_info[0] >= parameter_end) {
        char* cpu_string_ptr = cpu_string;
    
        for (int parameter = 0x80000002; parameter <= parameter_end &&
             cpu_string_ptr < &cpu_string[sizeof(cpu_string)]; parameter++) {
          __cpuid(cpu_info, parameter);
          memcpy(cpu_string_ptr, cpu_info, sizeof(cpu_info));
          cpu_string_ptr += sizeof(cpu_info);
        }
        cpu_brand_.assign(cpu_string, cpu_string_ptr - cpu_string);
      }
    
      const int parameter_containing_non_stop_time_stamp_counter = 0x80000007;
      if (max_parameter >= parameter_containing_non_stop_time_stamp_counter) {
        __cpuid(cpu_info, parameter_containing_non_stop_time_stamp_counter);
        has_non_stop_time_stamp_counter_ = (cpu_info[3] & (1 << 8)) != 0;
      }
    #elif defined(ARCH_CPU_ARM_FAMILY) && (defined(OS_ANDROID) || defined(OS_LINUX))
      cpu_brand_.assign(g_lazy_cpuinfo.Get().brand());
      has_broken_neon_ = g_lazy_cpuinfo.Get().has_broken_neon();
    #endif
    }
    
    CPU::IntelMicroArchitecture CPU::GetIntelMicroArchitecture() const {
      if (has_avx()) return AVX;
      if (has_sse42()) return SSE42;
      if (has_sse41()) return SSE41;
      if (has_ssse3()) return SSSE3;
      if (has_sse3()) return SSE3;
      if (has_sse2()) return SSE2;
      if (has_sse()) return SSE;
      return PENTIUM;
    }

上面的代码中用到了\_\_cpuid，下面就行介绍介绍。

**\_\_cpuid**

功能：  
Generates the cpuid instruction available on x86 and x64, which queries the processor for information about the supported features and CPU type.

原型：

void __cpuid(
       int CPUInfo[4],
       int InfoType
    );

更多请关注：  
[https://msdn.microsoft.com/en-us/library/hskdteyh(VS.80).aspx][https_msdn.microsoft.com_en-us_library_hskdteyh_VS.80_.aspx]

\_\_cpuidex函数的InfoType参数是CPUID指令的eax参数，即功能ID。ECXValue参数是CPUID指令的ecx参数，即子功能ID。CPUInfo参数用于接收输出的eax, ebx, ecx, edx这四个寄存器。

用条件编译判断VC编译器对Intrinsics函数的支持性（\_MSC\_VER）。

**使用**

int main(int argc, char* argv[]) {
    
      base::CPU *cpu = new base::CPU();
      std::cout << cpu->cpu_brand() << std::endl;
      system("pause");
      return 0;
    }

输出：  
Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz

[Google_Chromium_base_stl_util]: http://blog.csdn.net/wangshubo1989/article/details/53558617
[Google_Chromium_base_windows_version]: http://blog.csdn.net/wangshubo1989/article/details/53576647
[https_msdn.microsoft.com_en-us_library_hskdteyh_VS.80_.aspx]: https://msdn.microsoft.com/en-us/library/hskdteyh%28VS.80%29.aspx