Re: AIX Large Pages and SMT4
- From: Stefan Koehler <contact@xxxxxxxx>
- To: neil_chandler@xxxxxxxxxxx, Oracle-L@xxxxxxxxxxxxx
- Date: Fri, 25 Oct 2019 13:17:09 +0200 (CEST)
Hello Neil,
Does anyone have any input on whether to use medium pages or large pages on
AIX in relation to performance?
Since Oracle 11g medium (64k) page size is used by default - so the question
would be more like any benefit from 64k to 16 MB page size. In general I would
advise to use large pages as I have seen several performance improvements but
have also seen cases where it has close to 0 impact - however these systems
were not a real good candidate anyway because of highly I/O driven. It does not
hurt but can improve :)
By the way even IBM states it in some of its official papers, e.g.
http://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/WP102171
Does anyone have any input about using SMT2/4/8 usage - my slob testing has
seen slightly better throughput with SMT4 over SMT2 (SMT4 vs SMT8 was the
same)
My advice: Check your production workload and set SMT to 1 if
#num_of_session_on_cpu =< #amount_of_cores. You get the best single thread
performance with no SMT at all (
https://www.anandtech.com/show/10435/assessing-ibms-power8-part-1/4 & ;
https://www.ibm.com/developerworks/community/blogs/aixpert/entry/local_near_far_memory_part_3_scheduling_processes_to_smt_virtual_processors130
) - Oracle is mostly a single thread application and so don't waste possibly
available CPU instructions :-)
As soon as you have more processes on CPU than cores you benefit from higher
SMT levels - however AFAIK the dispatching has slightly changed with Power 9
and I never did any benchmarks with that platform in this area.
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website:
http://www.soocs.de
Twitter: @OracleSK
Neil Chandler <neil_chandler@xxxxxxxxxxx> hat am 24. Oktober 2019 um 10:48
geschrieben:
Hi,
A couple of Oracle (11.2.0.4 and 19) on AIX (7.2) questions:
Does anyone have any input on whether to use medium pages or large pages on
AIX in relation to performance? I'm primarily concerned about performance -
especially when the server is stressed.
Does anyone have any input about using SMT2/4/8 usage - my slob testing has
seen slightly better throughput with SMT4 over SMT2 (SMT4 vs SMT8 was the
same) but my testing has been limited to this point and is far from
conclusive.
Neil Chandler.
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