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[Andy Whitcroft <apw@xxxxxxxxxxxxx>]

Note these patches have been found to cause crashes and have been
reverted under Bug #1398596.

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https://bugs.launchpad.net/bugs/1358949

Title:
  arm64 iperf performance suboptimal

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Trusty:
  Fix Released
Status in linux source package in Utopic:
  Fix Released

Bug description:
  [Impact]
  The copy_{to,from}_user implementations in the Ubuntu kernel are suboptimal. Optimized implementations have been submitted upstream and have shown a significant improvement in network performance.

      Iperf performance increase:
                  -l (size)               1 core result
      Optimized   64B                     44-51Mb/s
                  1500B                   4.9Gb/s
                  30000B                  16.2Gb/s
      Original    64B                     34-50.7Mb/s
                  1500B                   4.7Gb/s
                  30000B                  14.5Gb/s

  [Test Case]
  Generate traffic from one node to another using iperf (see above for config).

  [Regression Risk]
  These functions are obviously used heavily throughout the kernel, so a defect here could have significant impact. This risk is mitigated by using an implementation heavily based on the linaro string libraries (which are used in other places already, e.g. glibc), and through active testing of this patch on real hardware using a trusty-kernel base.

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