我已经发送了许多http请求与周期

WebRequest request = (WebRequest)WebRequest.Create(str);

在我的计算机上，这条线大约需要500ms

WebResponse response = request.GetResponse();

在网络上的其他计算机上：10至20毫秒
如何修复这个bug？网络上的其他计算机更快地完成请求可能有什么原因？
未安装代理，请求发送到127.0.0.1:port。
日志代码

String IdHTTPUt_Get(string str)
         {
            string res="";
             
DateTime dt = DateTime.Now;
             
WriteLog("begin");
           
WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
           
 WebRequest request = (WebRequest)WebRequest.Create(str);
            
WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
             
request.Credentials = new NetworkCredential(opt_Utor_User,opt_Utor_Password);

request.Method = "GET";
            
WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
           
request.Proxy = null;
            
using (WebResponse response = request.GetResponse())
           
{
                
  WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
                
  Stream receiveStream = response.GetResponseStream();
                
  WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
                
  StreamReader readStream = new
 
  StreamReader(receiveStream,Encoding.UTF8);
               
  WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
                
  res = readStream.ReadToEnd();
                
  WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
                
  receiveStream.Close();                 
  readStream.Close();
             
}
            
WriteLog((DateTime.Now - dt).ToString()); dt = DateTime.Now;
           
return res;

  }