内核线程和用户态进程的cpu利用率过高时的调试方法

--kworker

What is kworker? 

kworker

 means
a Linux kernel process doing "work" (processing system calls). You can have several of them in your process list: 

kworker/0:1

 is
the one on your first CPU core, 

kworker/1:1

 the
one on your second etc..

Why does kworker hog your CPU? To find out why a kworker is wasting your CPU, you can create CPU backtraces: watch your processor load (with 

top

 or
something) and in moments of high load through 

kworker

,
execute 

echo
l > /proc/sysrq-trigger

 to create a backtrace. (On Ubuntu, this needs you to login with 

sudo
-s

). Do this several times, then watch the backtraces at the end of 

dmesg

 output.
See what happens frequently in the CPU backtraces, it hopefully points you to the source of your problem.

Example: e1000e. In my case, I found a backtrace like this nearly every time:

Call Trace:
delay_tsc+0x4a/0x80
__const_udelay+0x2c/0x30
e1000_acquire_swflag_ich8lan+0xa2/0x240 [e1000e]
e1000e_read_phy_reg_igp+0x29/0x80 [e1000e]
e1000e_phy_has_link_generic+0x85/0x120 [e1000e]
e1000_check_for_copper_link_ich8lan+0x48/0x930 [e1000e]
e1000e_has_link+0x55/0xd0 [e1000e]
e1000_watchdog_task+0x5e/0x960 [e1000e]

It hinted me to a problem in the 

e1000e

 Ethernet
card module, and indeed a 

sudo
rmmod e1000e

made the high CPU load go away immediately [e1000e bug #26].

用户态进程：

可以使用kill -6 pid杀掉进程，产生一个core文件。多次执行后，基本上就能看出来哪段代码在占用cpu。