[Bug 1582181] Re: AArch64: slow cpuinfo due to redundant loop

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: lshw (Ubuntu)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/1582181

Title:
  AArch64: slow cpuinfo due to redundant loop

Status in lshw package in Ubuntu:
  Confirmed

Bug description:
  lshw on AArch64 hardware is painfully slow.
  This affects both lshw in current Ubuntu releases and vanilla upstream.

  For a 48 core node, cpuinfo parsing added up to 30 seconds (8 lines
  per core in /proc/cpuinfo add up to 384 lines to parse).

  For a 96 core node, parsing took up to 5 minutes (!).

  I think the problem was introduced by [1], and can be summarized as:
  - CPU capabilities should be added only to the current CPU core,
    and NOT to all previous CPU cores parsed.

  My suggestion is dropping the loop in [1], thus calling the <addHint>
  and <describeCapability> only for currentcpu.

  I put together a small patch (basically removing the for loop in question)
  at [2] (or see attachement), which should be applied on top of version
  "02.16-2ubuntu1.3" from Ubuntu Trusty 14.04.

  After applying the patch at [2], parsing for the above system (48 cores)
  takes less than 1 second (instead of 30s), with the exact same results ...

  [1]
  https://github.com/lyonel/lshw/commit/beb89de5a3c10449fe73f1c77b2486d868e5bc9a
  #diff-f4010714738fa4cdd5999499579da2b3R217

  [2] http://paste.ubuntu.com/16456620/

  # lsb_release -rd
  Description:    Ubuntu 14.04.4 LTS
  Release:        14.04

  BR,
  Alex

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