High CPU system usage

Glenn Steen glenn.steen at GMAIL.COM
Thu Aug 25 21:18:09 IST 2005

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On 25/08/05, Ugo Bellavance <ugob at camo-route.com> wrote:
> Glenn Steen wrote:
> > BTW, as one can see from the "new style" listing, you get hit a fair
> > bit on "/" too, perhaps something to look at...
> > If you decide to revert to ext2, take care with "/" and your initrd.
> > But you knew that:-).
> >
> I'm wondering what is reading/writing on '/'.

I was going to say "/tmp", but you have that separate too.... so this
might actually be your "clincher".Since it's mostly writing you might
be able to find out what gets written through the atime bit... some
"intelligent" find or just browsing with an appropriate ls. lsof might
also give a clue or two.

> Another thing that makes me wonder is the amount of idle CPU.  I just
> logged in as my server had a high load and I saw that even with many
> MailScanner processes running and using CPU, there was often significant
> Idle %. (10-30%).

Well, although generally IO is CPU-bound, you could see this if you
were exhausting your RAID-controllers write-cache.... I'm not too
familiar with the one you've got there (more used to SMARTs at the low
end and Clariions/FC on the "high" end), but if you have your cache
watermark levels wrong (for the IO patterns you see) you might see
rather "choppy" behaviour.... if you have such at all.
Also, write-cache mirroring can be a real performance killer. I
usually try to live with that though, safety first and all that:-).

Or it's something else altogether:-).
What did the top show?

-- Glenn
email: glenn < dot > steen < at > gmail < dot > com
work: glenn < dot > steen < at > ap1 < dot > se

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