PAPI doesn't work properly on Sandy Bridge when HT enabled in the BIOS

Solution Verified - Updated -

Issue

  • On machines with HT enabled in the BIOS some cores are taken off line in order to not make them available except to select users.
  • For certain applications one processor running at full speed is faster than two HT cores.
  • Taking the cores off line makes sure that the full resources of the core are available.
  • Found this difference in papi_avail output when running on HT-enabled nodes (compute nodes) vs. no-HT nodes (login nodes):
  • With HT-enabled:
Available events and hardware information.
--------------------------------------------------------------------------------
PAPI Version             : 4.2.0.0
Vendor string and code   : GenuineIntel (1)
Model string and code    : Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz (45)
CPU Revision             : 6.000000
CPUID Info               : Family: 6  Model: 45  Stepping: 6
CPU Megahertz            : 1200.000000
CPU Clock Megahertz      : 1200
Hdw Threads per core     : 1
Cores per Socket         : 8
NUMA Nodes               : 2
CPU's per Node           : 16
Total CPU's              : 32
Number Hardware Counters : 11
Max Multiplex Counters   : 64
  • Note that PAPI seems to be getting the threads-per-core wrong, though cores per socket is correct.
  • Also, while Total CPUs is 32, 16 of those, the HT CPUs are currently offline.
  • With HT-disabled:
Available events and hardware information.
--------------------------------------------------------------------------------
PAPI Version             : 4.2.0.0
Vendor string and code   : GenuineIntel (1)
Model string and code    : Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz (45)
CPU Revision             : 6.000000
CPUID Info               : Family: 6  Model: 45  Stepping: 6
CPU Megahertz            : 1200.000000
CPU Clock Megahertz      : 1200
Hdw Threads per core     : 1
Cores per Socket         : 8
NUMA Nodes               : 2
CPU's per Node           : 8
Total CPU's              : 16
Number Hardware Counters : 11
Max Multiplex Counters   : 64
--------------------------------------------------------------------------------

Environment

  • Red Hat Enterprise Linux 6

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