cpu usage too high, entire system sluggish, top is messed up

James Gray james at grayonline.id.au
Wed Jun 21 22:46:48 BST 2006


On Thursday 22 June 2006 01:38, Christopher J. Bottaro wrote:
> Hi,
>
> top is reporting cpu usage between 25 and 50% all the time.  The weird
> thing is that the process list isn't showing any processes using cpu that
> add up to 25 or 50%.  What is going on?  My system is very sluggish.

I am offline ATM, so I haven't had a chance to check your screen shot.  
However, from what you describe, it sounds like there is something chewing 
large amounts of I/O time.  This usually occurs when you use software-RAID 
(lvm, evms, etc) on slow CPU's or when there is a lot of disk/network/etc I/O 
and whatever device is being hammered isn't in DMA mode - thus everything 
goes via the CPU.

> Here is a screenshot of top to show what I'm talking about:
> http://i6.tinypic.com/15573ev.png
>
> Notice the cpu usage is over 50%, but the process list isn't showing any
> processes using nearly that much.  It's like that all the time and it's
> making my whole system very sluggish.

Yep - if it's the kernel waiting for a device to return control/data back then 
it wont show up under the process' CPU usage but you will see it next to the 
"wa" in top.

> I'm using an Centrino based laptop if that offers any insight into the
> problem.  I noticed another person having laptop issues on this list...

I also have a Centrino-based laptop and found that the last Breezy kernel 
update caused all manner of problems with loosing interrupts etc every time 
the CPU changed frequency.  Bah.  Problem went away with Dapper but it blew 
up on Tuesday and is no more (long story, and not Ubuntu's fault either - 
PEBKAC)

Cheers,

James
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