为什么当我的erlangtcp代理得到许多并发请求时性能会下降这么多?

为了便于学习,我用Erlang编写了一个简单的TCP代理。它可以工作,但当我使用ab(apachebench)发出许多并发请求时,我遇到了一个奇怪的性能下降。我想知道的不是性能下降本身,而是下降的幅度。后端是nginx作为web服务器。我的代理人在ab和nginx之间。

这是我代理人的密码。

-module(proxy).
-export([start/3]).

start(InPort, OutHost, OutPort) ->
  {ok, Listen} = gen_tcp:listen(InPort, [binary, {packet, 0}, {active, once}]),
  spawn(fun() -> connect(Listen, OutHost, OutPort) end).

connect(Listen, OutHost, OutPort) ->
  {ok, Client} = gen_tcp:accept(Listen),
  spawn(fun() -> connect(Listen, OutHost, OutPort) end),
  {ok, Server} = gen_tcp:connect(OutHost, OutPort, [binary, {packet, 0}, {active, once}]),
  loop(Client, Server).

loop(Client, Server) ->
  receive
    {tcp, Client, Data} ->
      gen_tcp:send(Server, Data),
      inet:setopts(Client, [{active, once}]),
      loop(Client, Server);
    {tcp, Server, Data} ->
      gen_tcp:send(Client, Data),
      inet:setopts(Server, [{active, once}]),
      loop(Client, Server);
    {tcp_closed, _} ->
      ok
  end.

在我的代理上触发64个连续的请求,我得到了一个非常好的结果。

ab -n 64 127.0.0.1:80/

Concurrency Level:      1
Time taken for tests:   0.097 seconds
Complete requests:      64
Failed requests:        0
Write errors:           0
Total transferred:      23168 bytes
HTML transferred:       9664 bytes
Requests per second:    659.79 [#/sec] (mean)
Time per request:       1.516 [ms] (mean)
Time per request:       1.516 [ms] (mean, across all concurrent requests)
Transfer rate:          233.25 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.3      0       1
Processing:     1    1   0.5      1       2
Waiting:        0    1   0.4      1       2
Total:          1    1   0.5      1       2

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      2
  75%      2
  80%      2
  90%      2
  95%      2
  98%      2
  99%      2
 100%      2 (longest request)

它只是比直接对nginx使用apachebench慢一点。

ab -n 64 -c 64 127.0.0.1:80/

Concurrency Level:      64
Time taken for tests:   2.011 seconds
Complete requests:      64
Failed requests:        0
Write errors:           0
Total transferred:      23168 bytes
HTML transferred:       9664 bytes
Requests per second:    31.82 [#/sec] (mean)
Time per request:       2011.000 [ms] (mean)
Time per request:       31.422 [ms] (mean, across all concurrent requests)
Transfer rate:          11.25 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0   31 121.7      0     501
Processing:     3 1135 714.4   1001    2006
Waiting:        3 1134 714.3   1000    2005
Total:          3 1167 707.8   1001    2006

Percentage of the requests served within a certain time (ms)
  50%   1001
  66%   1502
  75%   2003
  80%   2004
  90%   2005
  95%   2005
  98%   2005
  99%   2006
 100%   2006 (longest request)

问题出在哪里?我本以为会有更低的表现,但为什么会有这么多呢?看看每秒的请求数!

我是否使用+a给erl提供了很多线程似乎无关紧要。我甚至尝试了SMP,但结果几乎相同。

我的设置:Windows764,英特尔四核,8GB内存。我在Ubuntu上使用128个并发请求得到了类似的结果。

编辑:包括新见解。请求的总数并不重要。这只是并发请求的计数。