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Old 08-20-2010, 12:52 AM   #1
elainelaw
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CPU usage over 100%


I use "top" to check the existing resource , but I found that the CPU usage over 100% ( eg. 100.1 , 100.8 ) , can advise what is wrong , is it normal ?

besides , can I control the maximum % of CPU usage , for example , it I want all process can not use more that 50% CPU , what can i do ? thx
 
Old 08-20-2010, 01:01 AM   #2
EricTRA
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Hi,

When you're looking at top then you can definetely see which process(es) are 'eating up' your CPU. If it's constantly at 100% then you do have a problem. You can try restarting the process that's consuming all CPU and see if that helps. Providing more information about what process(es) are putting it at 100% would be very usefull.

Kind regards,

Eric
 
Old 08-20-2010, 01:21 AM   #3
syg00
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Top is a sampler - rounding error, especially at the boundaries, is always a possibility.

For limiting particular processes, have a look at cpulimit - a userland solution.
cgroups is also an option.
 
Old 08-20-2010, 03:28 AM   #4
elainelaw
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thx reply , but why the CPU usage over 100% ?
 
Old 08-20-2010, 03:31 AM   #5
EricTRA
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Hi,

That's hard to say if you don't specify which process is putting your CPU at 100%. Can you post some output of the top command or at least which process is consuming your CPU as asked in my previous post?

Kind regards,

Eric
 
Old 08-20-2010, 03:46 AM   #6
druuna
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Hi,

Are we actually talking about a single cpu/core or multiple cpu's/cores? I've seen top show 390% cpu usage on a quad core cpu.

Top shows single state by default (all cpu's/cores together), press 1 (one) to see separate view. As syg00 already mentioned, rounding "errors" do make it possible to show slightly over a 100% for 1 specific cpu.

Hope this helps.
 
Old 08-20-2010, 07:18 AM   #7
MTK358
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On my multi-core CPU, if a process hogs the CPU it only takes one core to 100% and the others are free, even if there is something wrong with the process and it shouldn't be using so much CPU.
 
Old 08-21-2010, 09:02 PM   #8
chrism01
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If the mis-behaving proc was multi-threaded it could peg all the cores ...
 
Old 08-21-2010, 09:05 PM   #9
MrCode
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Perhaps one process is thrashing one core, and the other(s) is (are) experiencing idle activity? Rarely is a CPU truly at rest...

As for me, top averages the loads of the virtual cores into a single "system load" indicator, i.e. it shows around 25% when one virtual core is totally busy. I say "virtual" because this system's CPU is an Intel Core i5, which is multithreaded dual-core. Two physical cores, but the OS sees four.

Last edited by MrCode; 08-21-2010 at 09:09 PM.
 
Old 08-21-2010, 09:11 PM   #10
MTK358
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For example I have a quad-core CPU with hyper-threading, so the OS sees 8 CPUs. So even when the CPU is at 12.5% that means that a process is hogging the CPU or got stuck in an infinite loop.
 
Old 08-21-2010, 09:14 PM   #11
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Quote:
I have a quad-core CPU with hyper-threading, so the OS sees 8 CPUs
[OT]Do you ever really use all that computing power? A Core i7 would be awesome for mass virtualization...this machine maxes out if I have 3 VMs booting/highly loaded at once. [/OT]
 
Old 08-22-2010, 07:38 AM   #12
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Quote:
Originally Posted by MrCode View Post
[OT]Do you ever really use all that computing power? A Core i7 would be awesome for mass virtualization...this machine maxes out if I have 3 VMs booting/highly loaded at once. [/OT]
Not really, but sometimes I have a VM or two in the background and am compiling something.
 
  


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