Conference call notes 20171011

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Notes on the 87th EasyBuild conference call, Wednesday October 11th 2017 (5pm - 5.30pm CEST)

Attendees

Alphabetical list of attendees (6):

• Damian Alvarez (JSC, Germany)
• Alan O'Cais (JSC, Germany)
• Markus Geimer (JSC, Germany)
• Fotis Georgatos (Illumina, UK)
• Kenneth Hoste (HPC-UGent, Belgium)
• Davide Vanzo (Vanderbilt University)

Agenda

• update on next EasyBuild release
• enabling vectorisation in GCC
• override architecture flags in easyconfig files
• Q&A

Notes

Outlook to next EasyBuild release

• ETA: EasyBuild v3.4.1 by mid next week
• only a couple of minor things to be taken care of
  • framework done: https://github.com/easybuilders/easybuild-framework/milestone/51
  • easyblocks: https://github.com/easybuilders/easybuild-easyblocks/milestone/43
  • easyconfigs: https://github.com/easybuilders/easybuild-easyconfigs/milestone/46

Enabling vectorization in GCC

• Damian: auto-vectoriser is not enabled at -O2 for GCC
  • Intel does enable auto-vectoriser at -O2
  • no loop vectorisation being done for GCC without asking for it...
  • -ftree-vectorize (enabled automatically with -O3)
  • currently best option is to include it via --optarch
  • not enabled by -march=native
• should we enable it by default?
  • important for Skylake, KNL, ... (AVX512)
  • or allow site-specific config to always have it enabled
• should there be a toolchain option for it?
• how to test this?
  • benchmarks like Prime95?
  • https://www.mersenne.org/download/
  • Damian has plans to test this...
• configuration option to control/augment compiler flags used by EasyBuild
  • --cflags, --cxxflags, --fflags + also --optflags for generic flags
  • flags will be compiler-specific, see also how this is handled for --optarch (http://easybuild.readthedocs.io/en/latest/Controlling_compiler_optimization_flags.html#setting-architecture-flags-for-different-compilers-via-optarch-compiler-flags-compiler-flags)

Override architecture flags in easyconfig files

• way to opt-out for specific software packages?
• Damian: equivalent to --optarch for use in easyconfigs?
• use case:
  • using KNL builds on Haswell (for example for instrumentation with Score-P, etc.)
  • doesn't work if binary was built for KNL (AVX512)
    • cfr. check injected by Intel compilers
• Fotis: can we support logic rather than hardcoded values?
  • allow passing a Python module that determines arch flags to use
    • shouldn't be too hard... (famous last words)
  • also ties in with request to support plugins/hooks
  • Markus: for reproducibility, the archived easyconfigs should have hardcoded values in them
    • first step would be to add support 'optarch' easyconfig parameter anyway?
  • another option is to support providing a configuration file to --optarch
    • with additional filter for software packages, etc.
• Markus: for some packages, you'd like to enable arch-specific flags for some binaries, but not for others...
  • hard to do without proper support from build procedure used by package
  • -axHost vs xHost compiler option
    • Damian: results in 'fat' binaries with checks per function

Other

• X11: clean up way autogen.sh is called, avoid conditional?
  • see discussion on mailing list, subject "xorg-macros error install"
• Fotis: march target reported by GCC is not sufficient, better way?
  • changes between versions...
  • self-picked tags like 'sandybridge' may be sufficient?
  • Davide: interesting in good ways to 'tag' architectures
  • code provided by Fotis:

CPU_FLAGS_LIST="lm sse sse4_2 f16c avx avx2 avx512 avx512f avx512dq avx512cd avx512bw avx512vl eagerfpu epb ida epb fma"
## expand as needed
cpuflags="$(grep ^flags /proc/cpuinfo |uniq|cut -d: -f2-|xargs -n1|sort|comm -1 -2 - <(echo $CPU_FLAGS_LIST|xargs -n1|sort)|xargs|sed 's/ /:/g;s/$/:/g;s/^/:/g')"
march="$(gcc -march=native -Q --help=target | awk 'BEGIN { march="NA" } ; /^\ *-march= / { march= } END { print march }')" ## changes among GCC/4.8 vs 4.9
unset CPU_FLAGS_LIST

• Markus: anyone working on supporting the Clang Fortran compiler?
  • not really, other than briefly looking at it...
  • https://github.com/flang-compiler/flang
    • separate project for now, under development, aim is to include it in Clang
    • PGI Fortran frontend integrated with Clang, code generation done by LLVM backend
  • alternative to dragonegg LLVM plugin
• Davide: presentation area at SC17 at Vanderbilt booth, could set up EasyBuild presentations
  • also social meetup?
  • will contact mailing list