Table of Contents Description References Cheat sheet list of commands used Performance

I've written down a few reference notes on the steps I took to sort out the fixes needed for the bug report #2051 at the OpenFOAM bug tracker.

The following links have the details I used on Ubuntu 16.04:

• Downloaded the image "Full desktop image based on Debian Jessie, Version: May 2016" from here: https://www.raspberrypi.org/downloads/raspbian/
• Instructions on how to use QEmu: https://wiki.debian.org/RaspberryPi/qemu-user-static
  • I didn't notice an important detail that is given here: https://www.raspberrypi.org/forums/viewtopic.php?p=298537
• Reference notes on what to keep a look out for: http://sentryytech.blogspot.pt/2013/02/faster-compiling-on-emulated-raspberry.html
• Speed references, to ensure that I can get top performance: http://raspberrypi.stackexchange.com/questions/333/how-does-speed-of-qemu-emulation-compare-to-a-real-raspberry-pi-board

Base set-up:

    mkdir -p /home/VMMachines/Raspberry/Raspbian_Jessie/mnt
    cd /home/VMMachines/Raspberry/Raspbian_Jessie/
    unzip ~/Downloads/Linux\ ISOs/Raspbian/2016-05-27-raspbian-jessie.zip
    fdisk -lu 2016-05-27-raspbian-jessie.img

    dd if=/dev/zero bs=10M count=1024 >> 2016-05-27-raspbian-jessie.img
    sudo losetup -f -P --show 2016-05-27-raspbian-jessie.img

    sudo parted /dev/loop0
      print
      rm 2
      mkpart primary ext4 71,3 -1  #not 100% certain here of the order
      print

    sudo e2fsck -f /dev/loop0p2
    sudo resize2fs /dev/loop0p2
    sudo losetup -d /dev/loop0

Mounting image and getting ready before jail-rooting it:

    sudo losetup -f -P --show 2016-05-27-raspbian-jessie.img
    sudo mount /dev/loop0p2 -o rw $PWD/mnt

    cd mnt
    sudo cp /usr/bin/qemu-arm-static usr/bin/

    cp /etc/network/interfaces etc/network/interfaces
    cp /etc/resolv.conf etc/resolv.conf
    sed -i -e 's=^=#=' etc/ld.so.preload

Starting jail_root:

    sudo mount --bind /dev dev/
    sudo mount --bind /sys sys/
    sudo mount --bind /proc proc/
    sudo mount --bind /dev/pts dev/pts

    sudo chroot . bin/bash

Wrapping up jail-root:

    exit

    sudo umount dev/pts
    sudo umount dev
    sudo umount sys
    sudo umount proc

    cd ..
    sudo umount mnt
    sudo losetup -d /dev/loop0

Using this command (source):

    time (echo '2^2^20' | bc > /dev/null)

It takes 3.5s in my AMD A10-7850k, while within the emulated chroot, it takes 20s. Which means that a build of OpenFOAM that takes 88 minutes on the real machine, using 4 pseudo-cores, will take roughly 8 hours to build within the emulated chroot.

In comparison with the stats given here, the jail-root emulation takes 0m6.187s, versus 0m5.310s given on that page... which means that the emulation on this machine is a bit slower than desirable... but at least I don't need to buy the hardware to do the tests.

Took the following time to build OpenFOAM:

    real	1193m6.982s
    user	4035m14.252s
    sys	15m57.900s

Sooo... instead of 8 hours, it took 20 hours with the emulated system.