SMT 8 for AIX 6.1

[owlmind]

According to documentation, smt 8 should work on power8 systems with aix 6.1 latest updates.
However my 6100-09-07-1614 lpar refuses to activate smt 8.


There is  apar and workaround. But it's for 6100-09-06 and should have been fixed. Workaround also doesn't work.

https://www-01.ibm.com/support/docview.wss?uid=isg1IV70923
http://www-01.ibm.com/support/docview.wss?uid=isg1IV68445

Has anyone managed to activate smt 8 on aix 6.1? There is almost no information about it anywhere.

[Michael]

I do not have a system to try this on - but first you must see if the partition is running in POWER8 mode.

If not, then the firmware (PHYP/FSP) do not recognize the ability in AIX 6.1.

From memory: SMT8 support was never added to AIX 6.1 - It did get added into AIX 7.1. In any case, I have not heard of anyone using SMT8 with AIX 6.1. As the documents you mention are from early and late 2015 - maybe there was an intent (so-called Statement of Direction) to add support for AIX 6.1 and/or the author was overly optimistic.

So: If it is possible - you will need a firmware from 2016 or later, the partition will need to be set to boot in POWER8 mode, and you will need to halt/activate to get into POWER8 mode if you are still in POWER7-compat mode.

However, I would question why you would want SMT8 mode (unless it is just curiosity). IMHO the best generic performance is achieved with SMT4 and/or SMT2 - depending on application. Still IMHO - ST (aka SMT1) and SMT8 are only for special applications that demand those extremes for optimal performance.

p.s. If you do get SMT8 running on AIX 6.1 - please correct me!

[owlmind]

firmware FW840.22 release date 2016/07/06

I have set "POWER8 mode" in the lpar's profile deliberately, but it starts "power7 mode" anyway.

We have oracle database and it's owners believe they can achieve better performance with smt 8 on their workload. We are going to upgrade to 7.2 anyway, but it will take some time. We were hoping to try smt 8 sooner. So it looks like it has to wait upgrade.

[Michael]

If it is starting in POWER7 mode - SMT8 is not available.

Some aspects of Oracle may run better in SMT8 - but I would wonder whether they are fully using SMT4 already.

You can get an indication of how many logical CPU are being used by looking at the output of lparstat

Code: [Select]

%user  %sys  %wait  %idle physc %entc  lbusy   app  vcsw phint
----- ----- ------ ------ ----- ----- ------   --- ----- -----
 59.9   4.8    0.0   35.3  0.26  65.6    6.9  3.63   483     3
  7.3   1.4    0.0   91.3  0.04   9.3    1.1  3.88   295     0

Assuming SMT=4 and vpm_throughput_mode settigs are on defaults:
- when lbusy <= 25(%) - generally running in ST (SMT1)
- when lbusy > 25(%) and <= 50 - generally running in SMT2
- when lbusy >= 50(%) - generally running in SMT4
- but only really USING SMT4 "heavily" when lbusy > 75

Hope this helps!

[owlmind]

Thank you for help.