Hi Ben, all --
We were discussing this just now. Chapel's here.numCores is actually
the number of hyperthreads, gotten from sysconf(_SC_NPROCESSORS_ONLN).
Other than scanning /proc/cpuinfo, is there a system-defined way under
linux to get the core count, as opposed to the hyperthread count?
Of course /proc/cpuinfo wouldn't work on non-linux systems, but maybe we
already have an accurate core count on such systems. I'm not sure. In
any case, improving the situation on linux would be a good start.
(We could presumably get the number of cores from hwloc. That seems
like overkill, but might at least to portable to all our targets.)
thanks,
greg
On Fri, 9 May 2014, Ben Harshbarger wrote:
Hi all,
I ran into an issue with hyper threading on OSX this morning, and after a
discussion with Brad some questions were posed that seem better suited for
a group discussion.
Currently numCores (at least on linux) includes the count for
hyper-threading. This introduces some ambiguity in the meaning of
‘here.numCores’ (physical vs. logical), and raises some questions:
- What should numCores represent?
- Should we separate the notion of physical cores and the amount of
parallelism in hardware (new variable/name)?
- What does this mean for dataParTasksPerLocale?
Hopefully this gets the ball rolling.
-Ben
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