[Qemu-devel] [Bug 1756807] Re: performance regression in qemu-user + proot

[Alistair Buxton]

I just tested the patch from
https://bugs.launchpad.net/qemu/+bug/1740219 and it fixes the problem
for me. Specifically I only tried the final patch of the series.

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https://bugs.launchpad.net/bugs/1756807

Title:
  performance regression in qemu-user + proot

Status in QEMU:
  New
Status in qemu package in Ubuntu:
  New

Bug description:
  To reproduce:

  1. Install qemu-user-static and proot
  2. Enter some arm chroot using them:

      proot -0 -q qemu-arm-static -w / -r chroot/ /bin/bash

  3. Run a command which normally takes a short but measurable amount of
  time:

      cd /usr/share/doc && time grep -R hello

  Result:

  This is over 100 times slower on 18.04 than it was on 16.04. I am not
  sure if proot or qemu is causing the problem, but proot version has
  not changed. Also note that on 16.04 I am using the cloud repo version
  of qemu, which is newer than 16.04 stock, but still older than 18.04.

  Although system 2 is lower spec than system 1, it should not be this
  much slower. No other software seems to be affected.

  If required I can supply a chroot tarball. It is essentially just a
  Debian bootstrap though.

  Logs:


  System 1: i7-6700 3.4GHz, 32GB RAM, 512GB Crucial MX100 SSD, Ubuntu 16.04
  qemu-arm version 2.10.1(Debian 1:2.10+dfsg-0ubuntu3.4~cloud0)
  proot 5.1.0

  address@hidden:~/rpi-ramdisk/raspbian$ proot -0 -q qemu-arm-static -w / -r 
root/ /bin/bash
  address@hidden:/# cd /usr/share/doc
  address@hidden:/usr/share/doc# time grep -R hello
  dash/copyright:Debian GNU/Linux hello source package as the file COPYING.  If 
not,

  real  0m0.066s
  user  0m0.040s
  sys   0m0.008s



  System 2: i5-5300U 2.30GHz, 8GB RAM, 256GB Crucial MX300 SSD, Ubuntu 18.04
  qemu-arm version 2.11.1(Debian 1:2.11+dfsg-1ubuntu4)
  proot 5.1.0

  address@hidden:~/rpi-ramdisk/raspbian$ proot -0 -q qemu-arm-static -w / -r 
root/ /bin/bash
  address@hidden:/# cd /usr/share/doc
  address@hidden:/usr/share/doc# time grep -R hello
  dash/copyright:Debian GNU/Linux hello source package as the file COPYING.  If 
not,

  real  0m24.176s
  user  0m0.366s
  sys   0m11.352s

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: qemu (not installed)
  ProcVersionSignature: Ubuntu 4.15.0-12.13-generic 4.15.7
  Uname: Linux 4.15.0-12-generic x86_64
  ApportVersion: 2.20.8-0ubuntu10
  Architecture: amd64
  Date: Mon Mar 19 07:13:25 2018
  InstallationDate: Installed on 2018-03-18 (0 days ago)
  InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180318)
  SourcePackage: qemu
  UpgradeStatus: No upgrade log present (probably fresh install)

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