使用了 socket 的 dns 缓存，为什么速度还变慢了呢

查了一下网上关于socket关于dns缓存的代码，希望提高网络请求的速度，
自己在代码中使用了以后，发现速度反倒慢了，为什么呢 下面的 100 个请求中，使用了缓存之后时间增加了 4 秒多， 10 个请求的时候，时间增加了 0.2 秒左右

# coding=utf-8
import requests
import time
import socket
_dnscache = {}

def _setDNSCache():
    """ DNS 缓存 """
    def _getaddrinfo(*args, **kwargs):
        if args in _dnscache:
            # print (str(args) + " in cache")
            return _dnscache[args]
        else:
            # print (str(args) + " not in cache")
            _dnscache[args] = temp_getaddrinfo(*args, **kwargs)
            return _dnscache[args]

    if not hasattr(socket, '_getaddrinfo'):
        temp_getaddrinfo = socket.getaddrinfo
        socket.getaddrinfo = _getaddrinfo

class TiebaSpider:
    def __init__(self,tieba_name):
        self.tieba_name = tieba_name
        self.headers = {
                "User-Agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36"
            }
    def get_url_list(self):
        url_temp = "https://tieba.baidu.com/f?kw=" + self.tieba_name + "&ie=utf-8&pn={}"
        url_list = [url_temp.format(i*50) for i in range(100)]
        return url_list

    def parse_url(self,url):
        print("now parsing url",url)
        response = requests.get(url,headers=self.headers)
        return response.content.decode()

    def run(self):
        url_list = self.get_url_list()
        for url in url_list:
            html_str = self.parse_url(url)

if __name__ == '__main__':
    t1 = time.time()
    _setDNSCache()
    tieba_spider = TiebaSpider("李毅")
    tieba_spider.run()
    print(time.time()-t1)