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Subject: [hwloc-users] distributing across cores with hwloc-distrib
From: Tim Creech (tcreech_at_[hidden])
Date: 2014-03-30 01:56:38


Hello,
  I would like to use hwloc_distrib for a project, but I'm having some
trouble understanding how it distributes. Specifically, it seems to
avoid distributing multiple processes across cores, and I'm not sure
why.

As an example, consider the actual output of:

$ hwloc-distrib -i "4 4" 2
0x0000000f
0x000000f0

I'm expecting hwloc-distrib to tell me how to distribute 2 processes
across the 16 PUs (4 cores by 4 PUs), but the answer only involves 8
PUs, leaving the other 8 unused. If there were more cores on the
machine, then potentially the vast majority of them would be unused.

In other words, I might expect the output to use all of the PUs across
cores, for example:

$ hwloc-distrib -i "4 4" 2
0x000000ff
0x0000ff00

Why does hwloc-distrib leave PUs unused? I'm using hwloc-1.9. Any help
in understanding where I'm going wrong is greatly appreciated!

Thanks,
Tim