[users at i-scream] libstatgrab on AIX: data mismatch between saidar and topas

Tue May 24 14:10:38 BST 2016

Hi Anderson,

No, this is not correct. The LPAR technology allows (and prefers) dedicated Resources per partition, for shared resources WPAR's are recommended. I never tried, but assume that shared resources for LPAR mean minimum and maximum of resources can be reserved on demand.

The difference you see has nothing to do with physical machine view vs. partition / logical view.

Von meinem iPhone gesendet

> Am 24. Mäi. 2016 um 14:51 schrieb Anderson Carlos Trindade <anderson.trindade at optimode.com.br>:
> 
> Hi Jens,
> 
> So, the point is:
> 
>    - libstatgrab is reporting the physical CPU usage. If libstatgrab shows something around 65% of Idle, it means that 65% of all physical resources are Idle.
> 
>    - on the other hand, the sample code is reporting the LPAR usage. If the sample code shows something around 20% of Idle, it means that LPAR has just 20% of the CPU dedicated to LPAR is available to LPAR usage
> 
> Is this understanding correct?
> 
> Considering I have one application running inside a LPAR and this application is consuming almost all CPU dedicated to LPAR (around 80%) but the physical host is using just 35% of CPU, If libstatgrab returns the physical usage, I can’t see from the libstatgrab perspective that the LPAR is almost 100% of CPU usage. Is that correct?
> 
> 
> 
> 
>> Em 24 de mai de 2016, à(s) 06:11, Jens Rehsack <rehsack at gmail.com> escreveu:
>> 
>> Hi Anderson,
>> 
>> the example is very explicit about the measurement - it normalizes the values when lparstats.type.b.shared_enabled - libstatgrab doesn't.
>> libstatgrab reports the physical cpu measure - which can lead to misinterpretion for shared resources (which is up to our knowledge always the case when physical resources are shared on a best effort way). So we decided against that (similar for zones (Solaris), Jails (BSD) and Containers (Linux)) until we find a tuit to analyze all available technologies and a reasonable way to deal with them.
>> 
>> Thanks for remind me :)
>> 
>> Best regards,
>> Jens
>> 
>>> Am 23.05.2016 um 18:54 schrieb Anderson Carlos Trindade <anderson.trindade at optimode.com.br>:
>>> 
>>> Hi Jens,
>>> 
>>> Thank you for reply!
>>> 
>>> As far as I know, topas seems to be an AIX utility (https://www.ibm.com/support/knowledgecenter/#!/ssw_aix_71/com.ibm.aix.cmds5/topas.htm), but I can’t tel you where the data displayed by topas is coming from.
>>> 
>>> But let’s forget topas for a moment.
>>> 
>>> I got a sample code from IBM site (https://www.ibm.com/support/knowledgecenter/#!/ssw_aix_53/com.ibm.aix.prftools/doc/prftools/prftools07.htm%23wq407), which uses perfstat to report cpu usage statistics.
>>> 
>>> Then, I compiled this sample code and run in parallel to saidar, each one in a separated SSH session. While saidar is reporting around 80% of Idle time and 10% of user time, the sample code above (based on perfstat) is reporting something around 35% of idle time and 60% of user mode usage. I recorded a screenshot and I can share with you If you prefer.
>>> 
>>> Considering that saidar and the sample code above are getting data from the same source, why are these statistics so different?
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>>> Em 23 de mai de 2016, à(s) 13:02, Jens Rehsack <rehsack at gmail.com> escreveu:
>>>> 
>>>> Hi,
>>>> 
>>>>> Am 23.05.2016 um 17:02 schrieb Anderson Carlos Trindade <anderson.trindade at optimode.com.br>:
>>>>> 
>>>>> Hello List,
>>>>> 
>>>>> I’m trying to understanding some differences between data reported by AIX utility topas and saidar.
>>>>> 
>>>>> On a given moment (almost in the same second), saidar report the following CPU usage:
>>>>> 
>>>>> CPU Idle: 88,28%
>>>>> CPU system: 4,72%
>>>>> CPU User: 7,00%
>>>>> 
>>>>> but topas report the following usage:
>>>>> 
>>>>> %Idle 35,8%
>>>>> %Kern 3,5%
>>>>> %User: 60,5%
>>>>> %Wait 0,2%
>>>>> 
>>>>> It seems that both utilities are using different sources of data, since the usage reported is very different.
>>>>> Please, could you help me to understand where these differences are coming from?
>>>> 
>>>> Well, I don't know where topas is fetching it's data from - and where your topas comes from (AIX Linux Tools? 3rd party repo?) ....
>>>> 
>>>> As you can see here https://github.com/i-scream/libstatgrab/blob/master/src/libstatgrab/cpu_stats.c#L162, libstatgrab is using perfstat - the IBM recommendation and the same source used by nmon.
>>>> See https://www.ibm.com/support/knowledgecenter/ssw_aix_53/com.ibm.aix.prftools/doc/prftools/prftools07.htm%23wq407 for more details about libperfstat.
>>>> 
>>>> The reason for enhancing libstatgrab by a former customer was the poor data quality of GNU tools on Unices (HP-UX, AIX, Solaris).
>>>> When I'm in doubt, I trust libstatgrab more than all GNU tools together >:-)
>>>> 
>>>>> my apologies in advance, because I'm very new on AIX world
>>>>> 
>>>>> This is a LPAR with 4 CPU’s
>>>> 
>>>> Best regards
>>>> --
>>>> Jens Rehsack - rehsack at gmail.com
>> 
>> --
>> Jens Rehsack - rehsack at gmail.com
> 