kernel-packages team mailing list archive

[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

Would it be possible for you to test the latest upstream kernel? Refer
to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest
v3.15 kernel[0].

If this bug is fixed in the mainline kernel, please add the following
tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag:
'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".


Thanks in advance.


[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.15-rc4-utopic/


** Changed in: linux (Ubuntu)
   Importance: Undecided => Medium

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

** Tags added: kernel-da-key precise

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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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