Re: % CPU Usage Monitoring

[Jim Oberholtzer <midrangel@xxxxxxxxxxxxxxxxx>]

I suspect there is some misunderstanding about the numbers presented in
WRKSYSSTS/DSPSYSSTS.

The CPU and faulting/paging rates are displayed for the elapsed time period
shown in "Elapsed Time".  So if that shows 00:5:28 then the observation is
for 5 minutes, 28 seconds and the data is aggregated for that amount of
time.  If the elapsed time is 00:00:01 the observation is one second.
Anything under about 5 minutes is going to give you inaccurate (and mostly
useless) information about the system.  Also, do not be pounding away on
the refresh key F5, since hitting that more than a couple of times during
the observation will have some effect on the numbers it produces.  Your job
is included, so if you work the system hard, it will show up......

If you are after averages over time then the API will give that to you,
just start the observation, wait 5 minutes, then call the API again without
the reset.  The system reports this information extremely well.

Building your own software to aggregate the performance data is fine, but
it won't be as accurate as what the system provides you.

Also remember that Performance Data Investigator is there to help you see
trends and diagnose performance issues.  Even if you do not have the
performance tools loaded you can still take the observations and review
them on another system.  IBM does that all the time, as do I.


Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


On Tue, Oct 15, 2019 at 9:55 AM Pieter Henrico via RPG400-L <
rpg400-l@xxxxxxxxxxxxxxxxxx> wrote:

> Hi
>
> I am not sure if anybody answered on this question yet.  I use the
> following to pull the CPU information, if that will be of any help:
>
> exec sql SELECT AVERAGE_CPU_UTILIZATION into :pCPUAVG
>          from TABLE(QSYS2.SYSTEM_STATUS('YES')) x;
>
> Check the link for more info:
> https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_74/rzajq/rzajqudf
> sysstatus.htm
> <https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_74/rzajq/rzajqudfsysstatus.htm>
>
> In the beginning I also struggled to compare the values with the
> DSPSYSSTS, but I came to trust the values retrieved with this SQL.
>
> Hope it helps.
>
> Pieter
>
>
> -----Original Message-----
> From: RPG400-L <rpg400-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Suren K
> Sent: Thursday, 22 August 2019 4:57 PM
> To: RPG programming on IBM i <rpg400-l@xxxxxxxxxxxxxxxxxx>
> Subject: Reg: % CPU Usage Monitoring
>
> Hi All,
>
> I am trying to monitor the CPU usage maximum utilization and minimum
> utilization when performing a process in iSeries. For this, i am storing
> the SYSSTS details into an outfile for every 1 second using the API
> QWCRSSTS - Format SSTS0200 - % processing unit used (Position from 33 to
> 36) as CPU usage.
>
> Some times it seems to be correct when i compare the value manually by
> checking the DSPSYSSTS command. But some time the API is providing the CPU
> usage more than 80% but when i look into DSPSYSSTS it will still showing
> CPU used only 20%.
>
> Am i not looking into the right place for CPU usage?
>
> Regards,
> Surender K
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