kernel-packages team mailing list archive

[Craig Magina <1508471@xxxxxxxxxxxxxxxxxx>]

** Description changed:

- From trusty through to vivid there is a copy_to/from_user patch that
- improved performance on the m400. This patch was not pushed into wily's
- 4.2 kernel as a new one was nearing upstream acceptance. That patch has
- now landed in linux-next and needs to be backported to wily's 4.2
- kernel.
+ [Impact]
+ The copy_{to,from}_user implementations in the Ubuntu kernel are suboptimal. Optimized implementations have been accepted upstream and have shown a significant improvement in network performance.
+ 
+ [Test Case]
+ Generate traffic from one node to another using iperf.
+ 
+ [Regression Risk]
+ These functions are obviously used heavily throughout the kernel, so a defect here could have significant impact. However, it has been accepted by upstream after some cycles of review. The backported patches have also been tested on real arm64 hardware.

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https://bugs.launchpad.net/bugs/1508471

Title:
  [SRU] arm64 performance regression in wily 4.2 kernel on m400 due to
  dropped patch

Status in linux package in Ubuntu:
  In Progress

Bug description:
  [Impact]
  Performance Regression.

  The copy_{to,from}_user implementations in the Ubuntu kernel are
  suboptimal. Optimized implementations have been accepted upstream and
  have shown a significant improvement in network performance. Previous
  Ubuntu releases included non-upstream versions of these patches, but
  they were dropped during the wily cycle.

  [Test Case]
  Generate traffic from one node to another using iperf.

  [Regression Risk]
  These functions are obviously used heavily throughout the kernel, so a defect here could have significant impact. However, it has been accepted by upstream after some cycles of review, and we have shipped earlier versions of it in every arm64 release prior to wily. The backported patches have also been tested on real arm64 hardware.

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