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[Bug 1557690] Re: s390/kconfig: CONFIG_NUMA without CONFIG_NUMA_EMU does not make any sense on s390x

To: kernel-packages@xxxxxxxxxxxxxxxxxxx
From: Dimitri John Ledkov <launchpad@xxxxxxxxxxxx>
Date: Thu, 17 Mar 2016 23:53:54 -0000
Reply-to: Bug 1557690 <1557690@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx

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

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https://bugs.launchpad.net/bugs/1557690

Title:
  s390/kconfig: CONFIG_NUMA without CONFIG_NUMA_EMU does not make any
  sense on s390x

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Xenial:
  Fix Committed

Bug description:
  == Comment: #0 - Hendrik Brueckner - 2016-03-15 06:33:03 ==
  For NUMA, ensure the setting of these kernel configuration for s390x:

  # CONFIG_NUMA_BALANCING_DEFAULT_ENABLED is not set
  CONFIG_NUMA_EMU=y
  CONFIG_EMU_SIZE=0x10000000

  
  CONFIG_NUMA without CONFIG_NUMA_EMU does not make any sense. s390 does not provide hardware topology information. However, we do support fake NUMA to improve performance issues seen with very large memory configurations. Therefore, CONFIG_NUMA_EMU has to be enabled.

  Given that we only support fake NUMA
  CONFIG_NUMA_BALANCING_DEFAULT_ENABLED should be disabled, since it
  moves pages without any benefit but costs additional cpu cycles.

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