[Users] simfactory's num-smt and max-num-smt options and hyperthreading

[Roland Haas]

Hello all,

simfactory's machine.ini files support options num-smt and max-num-smt
which is take to be related to simultaneous multithreading (ie
hyper-threadig on Intel CPUs).

However it is not clear to me how to use them properly (looking at
other .ini files and how simfactory uses them in its simlib.py source
file) in relation to ppn, num-threads etc.

My initial assumption would have been that ppn is the number of logical
cores present (ie the number of processors from /proc/cpuinfo) and that
I'd describe a stampede2-skx compute node (with hyperthreading) as:

ppn = 96
num-threads = 2 # best according to Jim Healy
max-num-threads = 96
max-num-smt = 2
num-smt = 1

yet with these settings doing a:

sim/bin/submit --procs 96 ...

requests only a single compute node while I would have hoped two
compute nodes (due to num-smt=1 being the default). I had a look at the
various computeX.ini files and philip.ini but did not find much that
helped me in them.

So assuming I would like to do the following:

* describe a stampede2-skx compute node to simfactory
* so that one can use hypterthreading if desired
* so that hyperthreading is off by default

how would I do so?

Side note: smt should be described on the ET wiki in the setting up a
new machine page once this has been settled.

Yours,
Roland

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