被gprof输出弄糊涂了——调用太多

Confused by gprof output -- too many calls?

本文关键字:调用 太多 弄糊涂 gprof 输出      更新时间:2023-10-16

我刚刚开始使用gprof来优化我的慢代码。我被一个输出弄糊涂了,希望你能帮助我。

在这里:

                0.01    0.46     500/500         System::Update() [2]
[3]     96.2    0.01    0.46     500         Verlet::Advance() [3]
                0.02    0.19   61000/61122       CalculateAcceleration(std::vector<Particle, std::allocator<Particle> > const&, int) [4]
                0.00    0.06  183000/244127      Vector3D::Vector3D() [8]
                0.00    0.06  305000/676956      Vector3D::Vector3D(Vector3D const&) [6]
                0.00    0.03  122000/122000      Particle::SetPosition(Vector3D const&) [18]
                0.00    0.03  122000/122000      Particle::SetVelocity(Vector3D const&) [19]
                0.02    0.01  183000/183000      Vector3D::LinearCombine(double, Vector3D, double) [23]
                0.00    0.03  549000/921083      Vector3D::~Vector3D() [14]
                0.00    0.00  122000/364484      Vector3D::AddToVector(Vector3D) [30]
                0.00    0.00   61000/182242      std::pow(double, int) [44]
                0.00    0.00   61000/303484      Vector3D::ScalarMultVector(double) [51]
                0.00    0.00   61500/7579826     std::vector<Particle, std::allocator<Particle> >::size() const [25]
                0.00    0.00  366000/366122      std::vector<Particle, std::allocator<Particle> >::operator[](unsigned int) [127]
                0.00    0.00  122000/365606      Particle::GetPosition() const [128]

我运行这个函数500次,而for循环的大小是122,所以61,000对应于每次运行执行一次,122,000到2,183,000到3,244,000到4和305,000到5。下面是循环:

    void Advance() {
        for(int i = 0; i < (int)Particles.size(); i++) {
            const Vector3D& CurrentR_NMinus1 = Particles[i].GetPosition();
            const Vector3D& CurrentR_N = Particles1[i].GetPosition();
            const Vector3D& CurrentA_N = CalculateAcceleration(Particles1,i);
            // Calculate R_N+1
            Vector3D CurrentR_NPlus1;
            CurrentR_NPlus1.AddToVector(CurrentR_N);
            CurrentR_NPlus1.LinearCombine(2, CurrentR_NMinus1, -1);
            CurrentR_NPlus1.LinearCombine(1, CurrentA_N, pow(StepSize,2));
            // Calculate V_N
            Vector3D CurrentV_N;
            CurrentV_N.AddToVector(CurrentR_NPlus1);
            CurrentV_N.LinearCombine(1,CurrentR_NMinus1,-1);
            CurrentV_N.ScalarMultVector(1/(2*StepSize));
            // Update
            Particles[i].SetPosition(CurrentR_N);
            Particles[i].SetVelocity(CurrentV_N);
            t0 += StepSize;
            Particles1[i].SetPosition(CurrentR_NPlus1);
            Particles1[i].SetVelocity(Vector3D());
            t1 += StepSize;
        }
    }

所有条目对我来说都是有意义的,除了一个:Vector3D(Vector3D const&)显然被调用了5次。但是代码里没有!它的孩子当然叫它,但我认为他们在gprof列表中有自己的条目。我的想法有什么缺陷?它是否与粒子[]是Vector3Ds的矢量有关?

很抱歉,如果这是一个明显的问题——我只是刚刚开始使用gprof,我也是一个c++新手。我还没能在网上找到答案,但是,所以我希望你能帮助我。

非常感谢您的时间!

这是Vector3D类类型对象的copy constructor。隐式调用复制构造函数的一种情况是,将现有实例按值作为参数传递给函数。我的猜测是,这发生在对AddToVectorSetPositionSetVelocity的调用中,正如我在下面的评论中指出的那样,总共有5个调用。你可能很好奇为什么当你调用SetVelocity(Vector3D())时不调用copy constructor,这是最好的解释,如果你想知道,通过阅读这里的解释:

正确使用右值引用作为形参

const Vector3D& CurrentR_NMinus1 = Particles[i].GetPosition();
const Vector3D& CurrentR_N = Particles1[i].GetPosition();
const Vector3D& CurrentA_N = CalculateAcceleration(Particles1,i);
// Calculate R_N+1
Vector3D CurrentR_NPlus1;
CurrentR_NPlus1.AddToVector(CurrentR_N);          // copy constructor called
CurrentR_NPlus1.LinearCombine(2, CurrentR_NMinus1, -1);
CurrentR_NPlus1.LinearCombine(1, CurrentA_N, pow(StepSize,2));
// Calculate V_N
Vector3D CurrentV_N;
CurrentV_N.AddToVector(CurrentR_NPlus1);          // copy constructor called
CurrentV_N.LinearCombine(1,CurrentR_NMinus1,-1);  
CurrentV_N.ScalarMultVector(1/(2*StepSize));
// Update
Particles[i].SetPosition(CurrentR_N);             // copy constructor called
Particles[i].SetVelocity(CurrentV_N);             // copy constructor called
t0 += StepSize;
Particles1[i].SetPosition(CurrentR_NPlus1);       // copy constructor called
Particles1[i].SetVelocity(Vector3D());
t1 += StepSize;