[isabelle] isabelle build: number of threads



Dear all,

I started a build where with -v I got

  ISABELLE_BUILD_OPTIONS=""

  ML_PLATFORM="x86-linux"
  ML_HOME="/usr/local/Isabelle2013-2/contrib/polyml-5.5.1-1/x86-linux"
  ML_SYSTEM="polyml-5.5.1"
  ML_OPTIONS="-H 500"

and my ~/.isabelle/Isabelle2013-2/etc/settings is

  init_component "/usr/local/afp-2013-12-02/"
  ISAFOR="$HOME/rewriting/IsaFoR/"
  Z3_NON_COMMERCIAL="yes"

My processor is an i7-3630QM (4 cores, 8 threads; which are reported as 8 cores in /proc/cpuinfo ). So I would expect that by default 8 threads are used by "isabelle build". However, I get messages like the following

Timing <session-name> (4 threads, 44.314s elapsed time, 158.450s cpu time, 34.924s GC time, factor 3.58) Finished <session-name> (0:00:57 elapsed time, 0:02:56 cpu time, factor 3.08)

Indicating that only 4 threads are used. When I do the same thing on a different machine with an i7-3520M (2 cores, 4 threads) the corresponding messages are also saying "4 threads".

So my question is, how is the number of threads determined when ISASBELLE_BUILD_OPTIONS is empty?

cheers

chris




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