epoll vs poll

来源：互联网发布：centos下安装jdk1.7 编辑：程序博客网时间：2024/06/05 07:21

测试目的：证明epoll和poll在应用层相同的使用条件下，epoll的开销要明显的小于poll
Epoll采用ET模式

测试方法：
服务端，对连接过来的n个客户端只读取数据，系统调用只有poll和read, 或者epoll_wait和read, 便于分析。为了poll和epoll_wait调用的次数相等的目的，poll和epoll进程都采用相同的read策略，即读取fd发生EAGIAN或者读取的实际数据小于读取空间的数据。均采用非堵塞io

客户端，采用长连接接入后，不断发送数据, 采用堵塞方式。

测试行为：

客户端采用40个线程，不间断发送100字节，可以观察到网卡已经被占满

Iptraf检测到

Poll流量： 95165 kbits/s

Epoll流量： 97950 kbis/s

Poll:
系统调用占据了绝大多数的时间, 空闲很少
10:51:38 AM CPU   %user   %nice %system   %idle    intr/s
10:51:39 AM all    2.00    0.00   78.00   20.00 12362.00
10:51:40 AM all    2.00    0.00   75.00   23.00 12366.00
10:51:41 AM all    4.00    0.00   74.00   22.00 12355.00
10:51:42 AM all    0.00    0.00   83.00   17.00 12352.00
10:51:43 AM all    2.00    0.00   77.00   21.00 12341.00
10:51:44 AM all    4.00    0.00   80.00   16.00 12348.00
10:51:45 AM all    2.00    0.00   78.00   20.00 12350.00
10:51:46 AM all    1.00    0.00   82.00   17.00 12360.00
10:51:47 AM all    2.00    0.00   80.00   18.00 12365.00
10:51:48 AM all    4.00    0.00   82.00   14.00 12305.00
10:51:49 AM all    3.00    0.00   82.00   15.00 12309.00
10:51:50 AM all    2.00    0.00   81.00   17.00 12338.00
10:51:51 AM all    5.00    0.00   77.00   18.00 12339.00
10:51:52 AM all    2.00    0.00   80.00   18.00 12205.00
10:51:53 AM all    3.00    0.00   71.00   26.00 12324.00
10:51:54 AM all    2.00    0.00   74.00   24.00 12424.00
10:51:55 AM all    1.00    0.00   79.00   20.00 12356.00
10:51:56 AM all    3.00    0.00   78.00   19.00 12342.00
10:51:57 AM all    5.00    0.00   74.00   21.00 12337.00
10:51:58 AM all    2.00    0.00   79.00   19.00 12342.00
10:51:59 AM all    2.00    0.00   79.00   19.00 12336.00
10:52:00 AM all    6.00    0.00   70.00   24.00 12330.00
10:52:01 AM all    6.00    0.00   74.00   20.00 12334.00
10:52:02 AM all    3.00    0.00   74.00   23.00 12332.00
10:52:03 AM all    2.00    0.00   77.00   21.00 12374.00
10:52:04 AM all    3.00    0.00   77.00   20.00 12332.00
10:52:05 AM all    0.00    0.00   78.00   22.00 12339.00
10:52:06 AM all    0.00    0.00   80.00   20.00 12345.00
10:52:07 AM all    5.00    0.00   75.00   20.00 12355.00
10:52:08 AM all    3.00    0.00   77.00   20.00 12349.00
10:52:09 AM all    1.00    0.00   81.00   18.00 12350.00
10:52:10 AM all    3.00    0.00   76.00   21.00 12349.00
10:52:11 AM all    8.00    0.00   74.00   18.00 12376.00

Epoll:

10:55:30 AM CPU   %user   %nice %system   %idle    intr/s
10:55:31 AM all    2.00    0.00   23.00   75.00 12333.00
10:55:32 AM all    3.00    0.00   23.00   74.00 12374.00
10:55:33 AM all    3.00    0.00   24.00   73.00 12334.00
10:55:34 AM all    1.00    0.00   24.00   75.00 12352.00
10:55:35 AM all    5.00    0.00   21.00   74.00 12389.00
10:55:36 AM all    2.00    0.00   24.00   74.00 12351.00
10:55:37 AM all    2.00    0.00   25.00   73.00 12353.00
10:55:38 AM all    2.00    0.00   24.00   74.00 12341.00
10:55:39 AM all    2.00    0.00   24.00   74.00 12355.00
10:55:40 AM all    4.00    0.00   26.00   70.00 12370.00
10:55:41 AM all    2.00    0.00   24.00   74.00 12343.00
10:55:42 AM all    2.00    0.00   30.00   68.00 12337.00
10:55:43 AM all    0.00    0.00   26.00   74.00 12340.00
10:55:44 AM all    1.00    0.00   25.00   74.00 12341.00
10:55:45 AM all    0.00    0.00   26.00   74.00 12353.00
10:55:46 AM all    1.00    0.00   18.00   81.00 12346.00
10:55:47 AM all    1.00    0.00   27.00   72.00 12377.00
10:55:48 AM all    1.00    0.00   24.00   75.00 12361.00
10:55:49 AM all    1.00    0.00   27.00   72.00 12348.00
10:55:50 AM all    1.00    0.00   25.00   74.00 12345.00
10:55:51 AM all    1.00    0.00   30.00   69.00 12342.00
10:55:52 AM all    1.00    0.00   29.00   70.00 12343.00
10:55:53 AM all    2.00    0.00   23.00   75.00 12334.00
10:55:54 AM all    2.00    0.00   23.00   75.00 12340.00
10:55:55 AM all    2.00    0.00   21.00   77.00 12367.00
10:55:56 AM all    1.00    0.00   27.00   72.00 12363.00
10:55:57 AM all    1.00    0.00   23.00   76.00 12349.00
10:55:58 AM all    2.00    0.00   21.00   77.00 12340.00
10:55:59 AM all    1.00    0.00   22.00   77.00 12342.00
10:56:00 AM all    1.00    0.00   27.00   72.00 12352.00
10:56:01 AM all    2.00    0.00   24.00   74.00 12357.00
10:56:02 AM all    1.00    0.00   28.00   71.00 12346.00
10:56:03 AM all    3.00    0.00   24.00   73.00 12314.00

Top:

Poll:
22105 loki 16 0 852 848 756 R 56.9 0.3 1:07 0 pollserver
21802 loki 9 0 608 608 552 S 0.9 0.2 0:00 0 mpstat

Epoll:
22108 loki 14 0 904 900 808 R 9.9 0.3 0:24 0 epollserver
22110 loki 11 0 1168 1168 884 R 0.5 0.4 0:00 0 top

Strac
Poll的系统调用统计结果：
strace -c ./pollserver
execve("./pollserver", ["./pollserver"], [/* 28 vars */]) = 0
ServerTest listen success!
% time     seconds usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
54.95    8.240026          74    111511           poll
45.03    6.751312          19    347887           read

Epoll的系统调用统计结果：

% time     seconds usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
55.78    9.780626          30    323798           epoll_wait
44.20    7.749433          12    654077           read

Poll和epoll的I/O复用函数的调用比例基本是一致的，流量也是一样的，基本将网卡塞满

但是观察top,和mpstat的结果，明显epoll的系统调用要强于poll