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[Bug 1579205] Re: CONFIG_NR_CPUS=256 is too low

To: group.of.nepali.translators@xxxxxxxxxxxxxxxxxxx
From: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
Date: Thu, 08 Dec 2016 17:59:59 -0000
Reply-to: Bug 1579205 <1579205@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Xenial)
       Status: New => Fix Committed

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https://bugs.launchpad.net/bugs/1579205

Title:
  CONFIG_NR_CPUS=256 is too low

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

Bug description:
  Intel Knights Landing systems boot up to 272 processor cores. The
  stock Ubuntu Linux kernel images leave processor cores above 256
  disabled:

  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 256/0xeb ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 257/0xef ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 258/0xf3 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 259/0xf7 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 260/0xfb ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 261/0xff ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 262/0x103 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 263/0x107 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 264/0x10b ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 265/0x10f ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 266/0x113 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 267/0x117 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 268/0x11b ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 269/0x11f ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 270/0x123 ignored.
  [    0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached.  Processor 271/0x127 ignored.

  I'd request an increase in CONFIG_NR_CPUS to 512. This would match
  Debian's default setting. For comparison, RHEL/CentOS ship with 4096.

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