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Today I notice a very strange thing. One cpu core is always in 0 use .

Is it a bug?

Cpu0  :  0.0%us,  0.0%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,100.0%si,  0.0%st
Cpu1  : 37.7%us, 44.4%sy,  0.0%ni, 13.9%id,  2.6%wa,  0.0%hi,  1.3%si,  0.0%st
Cpu2  : 56.0%us, 17.9%sy,  0.0%ni, 13.6%id, 12.3%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu3  : 43.0%us, 40.4%sy,  0.0%ni, 13.2%id,  3.0%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu4  : 45.4%us, 13.9%sy,  0.0%ni, 29.8%id, 10.9%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu5  : 32.3%us, 47.5%sy,  0.0%ni, 16.8%id,  3.0%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu6  : 69.0%us, 12.5%sy,  0.0%ni, 15.8%id,  2.3%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu7  : 38.1%us, 42.4%sy,  0.0%ni, 18.2%id,  1.3%wa,  0.0%hi,  0.0%si,  0.0%st
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Are you running a single threaded program which is using that CPU? –  Hennes Dec 2 '12 at 19:00
    
I'm not sure which one can use a single cpu cure. I have mysql percona, nginx, apache, php –  teslasimus Dec 2 '12 at 19:06
    
Try top to see if there is a process with 100% CPU time. –  Hennes Dec 2 '12 at 19:17
    
top process has nothing to do with my question. –  teslasimus Dec 2 '12 at 19:22
    
What OS/kernel/distro? Do you have the irqbalance daemon running? That may impact this. Is this system physical or virtual? –  ewwhite Dec 2 '12 at 19:50
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3 Answers

up vote 11 down vote accepted

I don't see an idle CPU core in your output.

Core 0 is 100% active servicing software interrupts, all the others are split between user/system and idle.

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how can i find what software uses only one cpu? –  teslasimus Dec 2 '12 at 19:43
    
@teslasimus: That should be the subject of a new question. –  Iain Dec 2 '12 at 20:13
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That CPU isn't idle, if that's what you're thinking.

100.0%si shows that it's spending its time on handling interrupts.

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I know this is a old thread or this will answer your question but you can use

ps mo comm,psr

this will help you to find out in which processor the process is currently assigned to

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