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[Brad Figg <brad.figg@xxxxxxxxxxxxx>]

This bug is missing log files that will aid in diagnosing the problem.
>From a terminal window please run:

apport-collect 1315619

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable
to run this command, please add a comment stating that fact and change
the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.

** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1315619

Title:
  Job with 4 threads not assigned 4 distinct cores

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  On 12.04, I have reliably found that a job which starts 4 long-running
  threads on an otherwise-idle machine (there are some other threads
  which have been running for some time, but they have been kill
  -STOPped) gets the threads allocated to 4 distinct cores on my
  Haswell.

  On 14.04, I found that the threads were allocated to cores 0, 1, 5, 6
  - that is, two were running on the two hyper-threads 1 and 5 of the
  same core, and performance was 30% less than expected.  I can get
  around this with explicit taskset commands, but for my use case it's a
  serious regression from 12.04.

  I am not willing to disable hyperthreading, because it gives a large
  performance boost on other things I do on the same machine.

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