Re: Hardware tips

waiting for i/o indicates that a process that has reserved the cpu is waiting for the response of an I/O operation. On a single-cpu machine this can cause the machine to "virtually hang" because the process that's been executing has the cpu reserved and is just waiting.

Normally it can happen from time to time you have a peak of 90+, but if it returns at a regular interval, then you have a problem. try to backtrace what is causing the I/O. (eg. full table scan on big row ??? )

Maybe it's usefull in your case to gatherer the statistics a whole day long. ( with interval 10 sec )
then you will soon see if the "waiting for I/O" problem is indeed blocking your cpu.

your vmstat seems to be OK, but here the same remark, do a vmstat during a whole day.

Analyse the data. try to make correlations between high cpu-usage ( or high waiting for i/o ) and certain procedure, programs that have been runnning on the system.

Hope this helps
Gert

In article <GGmZ5.2040$pj.60898_at_news1.oke.nextra.no>,   "Sindre Solem" <sindre.solem_at_emmaedb.no> wrote:
>
> <denevge_at_my-deja.com> skrev i melding

 news:912vgu$g1a$1_at_nnrp1.deja.com...
> > execute the following : sar -u <interval> <number of samples>
> > eg sar -u 2 5 : this will give you 5 metrics.
> > Here you can see how the system is performing :
> > how many % of the cpu is given to user processes
> > how many % of the cpu is given to system processes
> > how many % of the cpu is waiting for i/o
> > how manu % of the cpu is idle
>
> Running this a few times I get values from 0 to 96 for waiting for
 i/o.
> Should it really get that high?
>
> > if you see a large "waiting for i/o" this means there could be a
> > bottleneck on the i/o performance.
> > If so, execute sar -q x y. Look at the run-queue. If it's +5, you
> > have a cpu performance problem. ( could be cause by a high "waiting
 for
> > i/o )
> > If "waiting for i/o" is high, check vmstat to see if you paging.
>
> vmstat gives these paging statistics:
> page
> re mf pi po fr de sr
> 0 21 26 0 0 0 0
>
> This means that nothing has been paged out, right?
>
>

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Before you buy. Received on Tue Dec 12 2000 - 08:17:09 CST