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If there is only one cpu and the IOwait is 99%, is the cpu still able to execute other processes, if so, is only 1% cpu resource could be used? or the other process could also use 100% cpu resource although under the scene of 99% Iowait.

I read the following line in one book" 

iowait is time spent receiving and handling hardware interrupts as a 
percentage of processor ticks.

If so, the 99% iowait doesn't mean the cpu is idle or waiting, actually it's very busy to receive and handle the interrupts. If this is true, I guess the other processes only have 1% cpu resource can be used.

Mike Devenney
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Jack
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    Processing hardware interrupts requires execution, so if 99% of the CPU cycles are used up on interrupt-handlers, then, (you are screwed), yes, only 1% is left over for everything else. – Martin James Aug 21 '15 at 17:49
  • Thji squestion is confusing anyway. Hardware interrupt-handlers do not have any process context and so there cannot be any 'other processes'. – Martin James Aug 21 '15 at 17:50

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I got the answer: The 99% IOWait means cpu almost 99% idle. i.e IOWait is a subset of cpu Idle. The following url has an excellent explanation: http://veithen.github.io/2013/11/18/iowait-linux.html

Jack
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  • That is inconsistent with the definition 'iowait is time spent receiving and handling hardware interrupts'. – Martin James Aug 21 '15 at 21:50
  • So I guess "iowait is time spent receiving and handling hardware interrupts" kind of wrong. The one represents the above statement is %si which means system interrupts percentage :) – Jack Aug 21 '15 at 21:56
  • Its the cpu % of processor needed for things witch disk is still looing for while cpu waiting at for disk IO to finish. How much free CPU waits for IO to give files! Basically all CPU is IDLE = 100% - USER processes % - SYSTEM processes % - NICE changed processes % (usually no one changes processes NICE priority so all of NICE processes will be 0) - IOWAIT how much processes waiting for files witch are waiting to be given to cpu OR idle process witch waits for HDD or SDD to finish reading, writing and giving to cpu like could be used 100 but used 10 cause other files slow - STEAL cpu lost. – Kangarooo Mar 23 '16 at 19:07