CPU usage over 100%

elainelaw · 08-19-2010, 11:52 PM

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

EricTRA · 08-20-2010, 12:01 AM

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

syg00 · 08-20-2010, 12:21 AM

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.

elainelaw · 08-20-2010, 02:28 AM

thx reply , but why the CPU usage over 100% ?

EricTRA · 08-20-2010, 02:31 AM

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

druuna · 08-20-2010, 02:46 AM

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.

MTK358 · 08-20-2010, 06:18 AM

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.

chrism01 · 08-21-2010, 08:02 PM

If the mis-behaving proc was multi-threaded it could peg all the cores ...

MrCode · 08-21-2010, 08:05 PM

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.

MTK358 · 08-21-2010, 08:11 PM

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.

MrCode · 08-21-2010, 08:14 PM

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]

MTK358 · 08-22-2010, 06:38 AM

Quote:

Originally Posted by MrCode

[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.