I've just asked a POWER8 hardware architect and he says that at least aix
has smt4 as default to avoid software scaling problems but it's better to
have the threads running rather than sleeping.
So enabling smt8 should either benefit or do nothing only in rare cases
would thread contention lower the system performance. Another thing is that
if you're running 80% or more cpu utilization you will see no benefit or
actually lower performance due to utilization getting too high.
I think that's all.
On how to enable smt8 I forgot to ask him...

Best Regards

On Sep 2, 2015 8:51 AM, <rob@xxxxxxxxx> wrote:

Have y'all played with SMT8 yet? I am running all Power 8's; two 814's
and one 824. They are running multiple LPARs: IBM i 7.1-15142-TR10, IBM
i 7.2-15135-TR2, VIOS, AIX, FW810.21 (108)

I've checked a few websites and I'm having a tough time just trying to
figure out how to turn it on.

I'm also trying to figure out if different lpars may benefit more than
others, or may it actually hurt performance on any.

First, I think we can safely assume that none of these lpars are a single
user machine which only runs one batch program at a time using traditional
I/O for ERP processing.
Many support Domino and/or WAS and many of these lpars are dedicated to
just such a workload.

Links I've read:

Rob Berendt
IBM Certified System Administrator - IBM i 6.1
Group Dekko
Dept 1600
Mail to: 2505 Dekko Drive
Garrett, IN 46738
Ship to: Dock 108
6928N 400E
Kendallville, IN 46755

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