一，前言

动手写linux驱动(3)--Apple的学习笔记已经写了一个阻塞，现在做一个非阻塞驱动，添加poll。

工程6是用select和poll，多路复用文件数量大，IO频繁的话用epoll，epoll最大的好处是不会随着fd数量增多而降低效率。只要epoll为什么好那么多我之前介绍过，网上有很多资料，原因比如用边沿触发，只通知一次，IO内存copy方式为mmap映射等。

工程6源码上传在gitee上https://gitee.com/applecai/linux-driver-study

二，遇到的问题

1. 刚刚写完select监控读和写的app后，top查看性能期望为0，结果为100%，查了下原因，因为我driver在无数据可读时会阻塞，也支持内容非满则阻塞。我用select同时监控读和写，由于先ioctl清空数据，所以一直可以写，导致一直在while中运行，没有机会sleep，才会看到性能100%。是个bug，对于我的fifo设计的driver，select只能监控同时监控一个，APP代码改成仅监控读即可。
2. timeout.tv_sec需要放在while循环中，FD_ZERO和FD_SET最好也放while中。否则只有第一次timeout设置有效，之后就不设置延迟监控了。

三，测试效果

select的timeout为5s，在5s内没有io写入动作，则休眠，作用top查看性能基本为0.

# ./applepaper6 /dev/applepaper6
[  519.383704] applepaper is set to zero
start
timeout
start
timeout
start
^C
# ./applepaper6 /dev/applepaper6 &
# [  533.386380] applepaper is set to zero
start
top
Mem: 20684K used, 482772K free, 44K shrd, 0K buff, 1964K cached
CPU:   0% usr   0% sys   0% nic 100% idle   0% io   0% irq   0% sirq
Load average: 0.00 0.00 0.00 1/51 128
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  128   109 root     R     1500   0%   0% top
  109     1 root     S     1536   0%   0% -sh
    1     0 root     S     1500   0%   0% init
   80     1 root     S     1492   0%   0% /sbin/syslogd -n
   84     1 root     S     1488   0%   0% /sbin/klogd -n
  127   109 root     S      688   0%   0% ./applepaper6 /dev/applepaper6
   49     2 root     IW       0   0%   0% [kworker/0:3-pm]
   60     2 root     IW<      0   0%   0% [kworker/u3:2-xp]
   48     2 root     IW       0   0%   0% [kworker/0:2-eve]
  120     2 root     IW<      0   0%   0% [kworker/u3:3-xp]
   64     2 root     IW       0   0%   0% [kworker/u2:5-rp]
    9     2 root     SW       0   0%   0% [ksoftirqd/0]
   10     2 root     IW       0   0%   0% [rcu_sched]
   61     2 root     IW       0   0%   0% [kworker/u2:2-rp]
    7     2 root     IW       0   0%   0% [kworker/u2:0-rp]
   59     2 root     IW<      0   0%   0% [kworker/u3:1-xp]
   45     2 root     IW       0   0%   0% [kworker/u2:1-rp]
   63     2 root     IW       0   0%   0% [kworker/u2:4-rp]
  119     2 root     IW<      0   0%   0% [kworker/u3:0-xp]
timeout   2 root     IW       0   0%   0% [kworker/u2:6-rp]
start
Mem: 20668K used, 482788K free, 44K shrd, 0K buff, 1964K cached
CPU:   0% usr   0% sys   0% nic  99% idle   0% io   0% irq   0% sirq
Load average: 0.00 0.00 0.00 1/51 128
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  109     1 root     S     1536   0%   0% -sh
    1     0 root     S     1500   0%   0% init
  128   109 root     R     1500   0%   0% top
   80     1 root     S     1492   0%   0% /sbin/syslogd -n
   84     1 root     S     1488   0%   0% /sbin/klogd -n
  127   109 root     S      688   0%   0% ./applepaper6 /dev/applepaper6
   49     2 root     IW       0   0%   0% [kworker/0:3-eve]
   60     2 root     IW<      0   0%   0% [kworker/u3:2-xp]
   48     2 root     IW       0   0%   0% [kworker/0:2-eve]
  120     2 root     IW<      0   0%   0% [kworker/u3:3-xp]
   64     2 root     IW       0   0%   0% [kworker/u2:5-rp]
    9     2 root     SW       0   0%   0% [ksoftirqd/0]
   10     2 root     IW       0   0%   0% [rcu_sched]
   61     2 root     IW       0   0%   0% [kworker/u2:2-rp]
    7     2 root     IW       0   0%   0% [kworker/u2:0-rp]
   59     2 root     IW<      0   0%   0% [kworker/u3:1-xp]
   45     2 root     IW       0   0%   0% [kworker/u2:1-rp]
   63     2 root     IW       0   0%   0% [kworker/u2:4-fl]
  119     2 root     IW<      0   0%   0% [kworker/u3:0-xp]
timeout   2 root     IW       0   0%   0% [kworker/u2:6-rp]
start

检查read效果，APP在后台运行，echo输入good job后可以通过select识别到并且打印出来。

# ./applepaper6 /dev/applepaper7 &
# [   74.832696] applepaper is set to zero

# echo "timeout
good job!"timeout
# echo "good job!" >/dev/applepaper7timeout

[   89.955800] written 10 bytes,current_len:10
[   89.960137] read 1 bytes,current_len:9
# [   89.966461] read 1 bytes,current_len:8
[   89.970293] read 1 bytes,current_len:7
[   89.974786] read 1 bytes,current_len:6
[   89.978589] read 1 bytes,current_len:5
[   89.982377] read 1 bytes,current_len:4
[   89.986819] read 1 bytes,current_len:3
[   89.990620] read 1 bytes,current_len:2
[   89.995005] read 1 bytes,current_len:1
[   89.998802] read 1 bytes,current_len:0
good job!

# timeout
top
Mem: 20800K used, 482656K free, 44K shrd, 0K buff, 1956K cached
CPU:   9% usr   0% sys   0% nic  90% idle   0% io   0% irq   0% sirq
Load average: 0.03 0.02 0.00 1/52 113
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  113   109 root     R     1500   0%   9% top
  109     1 root     S     1536   0%   0% -sh
    1     0 root     S     1500   0%   0% init
   80     1 root     S     1492   0%   0% /sbin/syslogd -n
   84     1 root     S     1488   0%   0% /sbin/klogd -n
  112   109 root     S      688   0%   0% ./applepaper6 /dev/applepaper7
   60     2 root     IW<      0   0%   0% [kworker/u3:2-xp]
   49     2 root     IW       0   0%   0% [kworker/0:3-nfs]
   48     2 root     IW       0   0%   0% [kworker/0:2-eve]
   15     2 root     IW       0   0%   0% [kworker/0:1-rcu]
   41     2 root     IW<      0   0%   0% [kworker/u3:0-xp]
   65     2 root     IW       0   0%   0% [kworker/u2:6-rp]
   10     2 root     IW       0   0%   0% [rcu_sched]
   64     2 root     IW       0   0%   0% [kworker/u2:5-rp]
    9     2 root     SW       0   0%   0% [ksoftirqd/0]
   13     2 root     SW       0   0%   0% [kdevtmpfs]
   45     2 root     IW       0   0%   0% [kworker/u2:1-rp]
    7     2 root     IW       0   0%   0% [kworker/u2:0-rp]
   59     2 root     IW<      0   0%   0% [kworker/u3:1-xp]
timeout   2 root     IW<      0   0%   0% [netns]