[Users] meeting minutes for 2017-03-20

[Roland Haas]

Present: Frank, Eloisa, Erik, Steve, Roland, Peter, Vassili, Ian,
Roberto

Failing tests:
* boostedpuncture failure likely due to code change
* GRHydro tests shows different behaviour depending on options, the
  test seems to fail only with new enough compiler, and -ffast-math
* affected hydro tests are very sensitive to data, it may be sufficient
  to use a mild increase in resolution
* as a general approach we need to decide if we want -ffast-math or if
  removing it does not affect results too much. It may be sufficient
  for gcc to specify options that allow the same subset of fast-math
  that icc uses by default
* if fast-math is needed for good performance, then we have to relax
  test constraints for these tests
* action items:
** run production benchmark with and without -fast-math on a modern
machine (Erik), use GW150914
** check if higher resolution helps for hydro tests (Roland)

piraha parser:
* Steve has an experimental version that produces multiple syntax
  errors for ccl files
* Ian would be happy with one good syntax error per ccl file and then
  an abort, Roland would prefer multiple ones. Most importantly
  multiple errors for par files
* if parsing speed is slow (Steve obtained a speedup for parallel
  parsing in a stand-alone parser but not with the integrated parser).
  May consider c++ parser with perl fallback if speed is an issue

KNL:
* can compile on stampede2, but fail to run with a segfault at startup
* Frank managed to compile in an interactive job and run
* Roland notes that NERSC's cori has custom modules/code to allow
  compilation of KNL code on the login nodes, what works on cori does
  not work for example on a different Cray machine (internal)
* wiki for progress
  https://docs.einsteintoolkit.org/et-docs/Running_Cactus_on_Knights_Landing
* Eloisa could obtain similar performance on KNL (~80%) for vacuum
  simulation as on Broadwel node
* CINECA has seminar on KNL, someone from Trento joined and we could try
  and ask them to give an ET seminar and report back

Yours,
Roland

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