Hi, we have a P5 9113-550 running AIX 5.3 that is showing the following:

kthr memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
0 0 189427 1795528 0 0 0 0 0 0 1 24 71 0 0 85 15

As you can see wait i/o is at 15 while nothing is being done. A quick glance
at the disk shows no activity either.

Here's an output per CPU by sar:

11:36:04 0 0 0 0 100 0.73
1 0 0 100 0 0.27
2 0 0 0 100 0.70
3 0 0 0 100 0.30
- 0 0 14 86 2.00

I've let it ran for a while and CPU1 ALWAYS display 100 for wait i/o.

Anybody knows what could be causing this or how to figure out what's causing
CPU1 to spend all its time waiting for I/O? Thanks.

Hi,
You met the Wait i/o percent while AIX had so little workload, so at least
you need to check the IO data by "iostat". Your case looks like mounting
some slower CD-like device, or using a little big page space.

Thanks.
Richard
"Sylvain Gagnon" <sylvain@myrealbox.com> wrote in message
news:ScnNe.23025$kz6.1222697@news20.bellglobal.com ...
> Hi, we have a P5 9113-550 running AIX 5.3 that is showing the following:
>
> kthr memory page faults cpu
> ----- ----------- ------------------------ ------------ -----------
> r b avm fre re pi po fr sr cy in sy cs us sy id wa
> 0 0 189427 1795528 0 0 0 0 0 0 1 24 71 0 0 85 15
>
> As you can see wait i/o is at 15 while nothing is being done. A quick
> glance at the disk shows no activity either.
>
> Here's an output per CPU by sar:
>
> 11:36:04 0 0 0 0 100 0.73
> 1 0 0 100 0 0.27
> 2 0 0 0 100 0.70
> 3 0 0 0 100 0.30
> - 0 0 14 86 2.00
>
> I've let it ran for a while and CPU1 ALWAYS display 100 for wait i/o.
>
> Anybody knows what could be causing this or how to figure out what's
> causing CPU1 to spend all its time waiting for I/O? Thanks.
>
>
>

We hav e the same thing on AIX 5.3.
When you turn off the smt option (The one that will let you see on
processor as two, not sure if it is really smt) You will see every
thing is normal.
This rathe strange thing happen in Power5 and Aix 5.3.1 combination.
I beleive it us a bug. Turning the Smt option is easy using smitty
system..
you do not have to boot.



Sylvain Gagnon wrote:
> Hi, we have a P5 9113-550 running AIX 5.3 that is showing the following:
>
> kthr memory page faults cpu
> ----- ----------- ------------------------ ------------ -----------
> r b avm fre re pi po fr sr cy in sy cs us sy id wa
> 0 0 189427 1795528 0 0 0 0 0 0 1 24 71 0 0 85 15
>
> As you can see wait i/o is at 15 while nothing is being done. A quick glance
> at the disk shows no activity either.
>
> Here's an output per CPU by sar:
>
> 11:36:04 0 0 0 0 100 0.73
> 1 0 0 100 0 0.27
> 2 0 0 0 100 0.70
> 3 0 0 0 100 0.30
> - 0 0 14 86 2.00
>
> I've let it ran for a while and CPU1 ALWAYS display 100 for wait i/o.
>
> Anybody knows what could be causing this or how to figure out what's causing
> CPU1 to spend all its time waiting for I/O? Thanks.