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["Christopher M. Penalver" <christopher.m.penalver@xxxxxxxxx>]

Valerio, thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:
apport-collect 1538040

** Package changed: linux-lts-wily (Ubuntu) => linux (Ubuntu)

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

** Changed in: linux (Ubuntu)
       Status: Confirmed => Incomplete

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https://bugs.launchpad.net/bugs/1538040

Title:
  Internal Hard drive extremely slow unless using barrier=0 on ext4

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  I have a brand new laptop (Asus N551VW, i7-6700HQ, 16 Gb ram) on which
  i installed Ubuntu 14.04 64bit and a new Samsung SSD 850 PRO 512Gb
  (latest firmware). I installed the default MySql 5.6.27 on the machine
  but I noticed a very VERY slow performance of the database (just
  creating a db and executing some migrations without any data takes
  around 33 seconds while on lower-hardware co-workers notebooks it
  takes like 3 seconds). Every sql statement seems to spend most time in
  "system lock" state, as i could see with a SHOW PROCESSLIST.

  I thought it to be an hard drive issue, but executing the hard drive
  benchmark in Ubuntu gives 500 Mb/s read and 350 Mb/s write speed,
  which looks mostly normal.

  I also tried updating to the new 4.2 kernel, but the issue still
  there. To make an experiment, i cloned the ssd on a normal hard drive,
  switched it in and connected the SSD externally with an usb box. I
  moved mysql data directory to the external disk, and retried the db
  creation: it took only 2.5 seconds.

  Just out of curiosity i tried the same operation on an internal non-
  ssd disk: when the hd is plugged inside the laptop with sata, the
  database creation takes more than 2 minutes, while with the data dir
  on external usb (with the same physical disk) it took less than 10
  seconds.

  To make it short, after some research, adding barrier=0 to the mount
  options of the root drive with no other modification caused the same
  script to take 1.5 seconds instead of 33, with a 22x increase in
  performance.

  I have opened his bug on askubuntu (http://askubuntu.com/questions/725182/ssd-extremely-slow-when-connected-with-internal-sata-ok-with-external-usb ) and it was suggested that this coud be an issue of the controller firmware/driver.
  The problem is present both in trusty's default kernel (3.19.0-47.53) and in the 4.2 (4.2.0-25.30).

  Let me know if you need more informations!

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-4.2.0-25-generic 4.2.0-25.30~14.04.1
  ProcVersionSignature: Ubuntu 4.2.0-25.30~14.04.1-generic 4.2.6
  Uname: Linux 4.2.0-25-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.14.1-0ubuntu3.19
  Architecture: amd64
  Date: Tue Jan 26 09:25:04 2016
  InstallationDate: Installed on 2016-01-06 (19 days ago)
  InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: linux-lts-wily
  UpgradeStatus: No upgrade log present (probably fresh install)

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