python-CherryPy 60x基准测试速度较慢,具有8个请求线程,而7个线程

2021-07-04 23:01:51

我很好奇为什么在使用ab和-c 7(7个并发线程)对Python Web服务器CherryPy进行基准测试时,它可以处理1500个请求/秒(大约是我的期望),但是当我更改为-c 8时,它下降到25个请求/秒.我在numthreads = 10上运行CherryPy(但如果我使用numthreads = 8或20则没有什么不同)在具有四个运行Python 2.6的64位Windows机器上.

我半怀疑Python GIL是问题的一部分,但是我不知道为什么只有当我有多达8个并发请求线程时才会发生.在四核计算机上,我希望它可能会在-c 4处更改,但事实并非如此.

我正在使用web.py随附的单文件CherryPy Web服务器,这是我要针对其进行测试的WSGI应用程序：

from web.wsgiserver import CherryPyWSGIServer

def application(environ, start_response):
    start_response("200 OK", [("Content-type", "text/plain")])
    return ["Hello World!",]

server = CherryPyWSGIServer(('0.0.0.0', 80), application, numthreads=10)
try:
    server.start()
except KeyboardInterrupt:
    server.stop()

7个和8个并发线程的ab输出为：

C:\\> ab -n 1000 -c 7 http://localhost/
...
Concurrency Level:      7
Time taken for tests:   0.670 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      130000 bytes
HTML transferred:       12000 bytes
Requests per second:    1492.39 [#/sec] (mean)
Time per request:       4.690 [ms] (mean)
Time per request:       0.670 [ms] (mean, across all concurrent requests)
Transfer rate:          189.46 [Kbytes/sec] received

C:\\> ab -n 1000 -c 8 http://localhost/
...
Concurrency Level:      8
Time taken for tests:   7.169 seconds
Complete requests:      158
Failed requests:        0
Write errors:           0
Total transferred:      20540 bytes
HTML transferred:       1896 bytes
Requests per second:    22.04 [#/sec] (mean)
Time per request:       362.973 [ms] (mean)
Time per request:       45.372 [ms] (mean, across all concurrent requests)
Transfer rate:          2.80 [Kbytes/sec] received

解决方法:

在我的linux机器上,这是由于从ab重传了TCP数据包,尽管我不确定为什么：

No.     Time        Source                Destination           Protocol Info                                                            Delta
  10682 21.218156   127.0.0.1             127.0.0.1             TCP      http-alt > 57246 [SYN, ACK] Seq=0 Ack=0 Win=32768 Len=0 MSS=16396 TSV=17307504 TSER=17306704 WS=6 21.218156
  10683 21.218205   127.0.0.1             127.0.0.1             TCP      57246 > http-alt [ACK] Seq=82 Ack=1 Win=513 Len=0 TSV=17307504 TSER=17307504 SLE=0 SRE=1 0.000049
  10701 29.306438   127.0.0.1             127.0.0.1             HTTP     [TCP Retransmission] GET / HTTP/1.0                             8.088233
  10703 29.306536   127.0.0.1             127.0.0.1             TCP      http-alt > 57246 [ACK] Seq=1 Ack=82 Win=512 Len=0 TSV=17309526 TSER=17309526 0.000098
  10704 29.308555   127.0.0.1             127.0.0.1             TCP      [TCP segment of a reassembled PDU]                              0.002019
  10705 29.308628   127.0.0.1             127.0.0.1             TCP      57246 > http-alt [ACK] Seq=82 Ack=107 Win=513 Len=0 TSV=17309526 TSER=17309526 0.000073
  10707 29.309718   127.0.0.1             127.0.0.1             TCP      [TCP segment of a reassembled PDU]                              0.001090
  10708 29.309754   127.0.0.1             127.0.0.1             TCP      57246 > http-alt [ACK] Seq=82 Ack=119 Win=513 Len=0 TSV=17309526 TSER=17309526 0.000036
  10710 29.309992   127.0.0.1             127.0.0.1             HTTP     HTTP/1.1 200 OK  (text/plain)                                   0.000238
  10711 29.310572   127.0.0.1             127.0.0.1             TCP      57246 > http-alt [FIN, ACK] Seq=82 Ack=120 Win=513 Len=0 TSV=17309527 TSER=17309526 0.000580
  10712 29.310661   127.0.0.1             127.0.0.1             TCP      http-alt > 57246 [ACK] Seq=120 Ack=83 Win=512 Len=0 TSV=17309527 TSER=17309527 0.000089

Wireshark也没有拾取原始的“ GET”数据包.由于某种原因,即使TCP连接是双AC的,ab也会尝试发送请求并失败.然后,客户端的TCP堆栈会等待几秒钟,以等待从未发送过的数据包进行ACK,然后,如果它没有看到ACK,则重试并成功.

就个人而言,我不会为此担心.如果有问题,那不是CherryPy的问题.它可能与ab的内部结构,使用HTTP / 1.0而不是1.1,缺少keepalive,使用localhost而不是实际的套接字(模拟某些网络流量的现实并忽略其他现实), Windows(眨眼),同一接口上的其他流量,在CPU上加载…列表不断.

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