C#怎样让不同的线程运行在不同的CPU上来提高运行效率？

1：假如单独调用FindShapeModel()方法执行所需要时间为100mms ;那我用多线程调用FindShapeModel()\FindShapeModel1()所用的时间应该也是100ms 左右，但实际测试发现会大于100*2ms ,偶尔有100ms左右的情况出现。
2：求解原因，代码中有设置让线程运行在不同的CPU上，但根据实没时间，好像还是运行在同一个CPU上。

3：FindShapeModel()\FindShapeModel1()方法内容一样的，只是名称不一样。
4：硬件配置 intel core(TM)-i7-7700 CPU

 private void FindShapeModel()

        {

            Thread.BeginThreadAffinity();



            IntPtr handle = GetCurrentThread();

            int id = Thread.CurrentThread.ManagedThreadId;

            uint id1 = GetCurrentThreadId();



            UIntPtr rtn = SetThreadAffinityMask(handle, new UIntPtr(0x000F));

            uint rtn1 = GetLastError();

            QueryPerformanceCounter(ref time[15]);

            isFinish[0]= FindShapeModel(hv_ModelID,ho_Image);



            Thread.EndThreadAffinity();



        }



        private void FindShapeModel1()

        {

            Thread.BeginThreadAffinity();



            IntPtr handle = GetCurrentThread();

            int id = Thread.CurrentThread.ManagedThreadId;

            uint id1 = GetCurrentThreadId();



            UIntPtr rtn = SetThreadAffinityMask(handle, new UIntPtr(0x0001));

            uint rtn1 = GetLastError();

            FindShapeModel1(hv_ModelID, ho_Image1);



            Thread.EndThreadAffinity();



        }

             MyThread[0] = new Thread(new ThreadStart(FindShapeModel));

            MyThread[0].Start();



            MyThread[1] = new Thread(new ThreadStart(FindShapeModel1));

            MyThread[1].Start();