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February 17, 2017 / ftth

Changing mysql nice priority on Ubuntu 16.04

I wanted to prioritize mysqld, and the only sources i could find were all referring to the nice parameter to mysqld_safe in /etc/mysql/my.cnf or hacking the /etc/init/mysql.conf. None of these worked for Ubuntu 16.04.

Systemd is now the init daemon for Ubuntu, so that’s the one who is launching it now:

root@easycast-myserver:~/bench# service mysql status
● mysql.service - MySQL Community Server
 Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
 Drop-In: /etc/systemd/system/mysql.service.d
 Active: active (running) since Fri 2017-02-17 10:40:04 CET; 5min ago
 Process: 8665 ExecStartPost=/usr/share/mysql/mysql-systemd-start post (code=exited, status=0/SUCCESS)
 Process: 8655 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 8664 (mysqld)
 CGroup: /system.slice/mysql.service
 └─8664 /usr/sbin/mysqld

So dropping the following systemd Nice option on the /etc/systemd/system/mysql.service.d/override.conf file did work:



Just restart the services:

systemctl daemon-reload && service mysql restart


October 14, 2016 / ftth

Building nvenc on Ubuntu 16.04

Took me a while to figure out, here’s a guide on building nvenc on Ubuntu 16.04:

  • apt-get install nvidia-cuda-dev nvidia-361 git pkg-config bison flex
  • apt-get build-deps gstreamer1.0-plugins-base gstreamer1.0-plugins-bad
  • download the 6.0 version of the nvidia video codec sdk (the Ubuntu 16.04 most recent driver is currently too old for the 7.0 version), unzip the sdk, copy the headers to /usr/local/include (sudo cp nvidia_video_sdk_6.0.1/Samples/common/inc/* /usr/local/include)
  • build a gst-uninstalled environment (see arun’s guide for instance), compiling gstreamer, gst-plugins-base should suffice
  • compile gst-plugins-bad with:
LDFLAGS="-L/usr/lib/nvidia-361/" ./configure --disable-gtk-doc --with-cuda-prefix="/usr"

Check that it’s working:

gst-launch-1.0 videotestsrc ! nvh264enc ! fakesink

Remember that the GPU must be Maxwell or Kepler (Fermi only supports decoding).

Many thanks to ystreet for his help on getting this right !

The theoretical proper way is the following, but it does not compile (see #772688) :

NVENCODE_CFLAGS="-I/home/user/src/nvidia_video_sdk_6.0.1/Samples/common/inc" NVENCODE_LIBS="-L/usr/lib/nvidia-361/" ./ --disable-gtk-doc --with-cuda-prefix="/usr" && make


October 6, 2016 / ftth

Tegra TK1 not booting after flashing from Arch Linux

I upgraded an Nvidia Jetson TK1 board to the 21.5 release, and it just never booted anymore. Accessing the RS232 using

sudo screen /dev/ttyUSB0 115200

indicated that the bootloader was not finding the internal sdcard.

The “solution” was to flash from Ubuntu 16.04 LTS and not Arch…


September 9, 2016 / ftth

Installing archlinux the EFI/systemd-boot way

I installed a fresh Arch system on an EFI enabled machine, and wanted to use the systemd bootloader (systemd-boot). While the Arch install guide is pretty much consise, it took me a few loops to make it work with UEFI/systemd.

The trick was to

  1. select the UEFI boot mode of the USB install drive (if not, /sys/firmware/efi/efivars is not mounted)
  2. create the partitions, ensuring that a big enough EFI  System Partition was present on the root drive (/dev/sda1) — by big enough, i mean that it should be at least 80 or 100 MB big because we’ll store the kernels here
  3. mount /dev/sda2 to /mnt and then mount /dev/sd1 to /mnt/boot before pacstrap
  4. after arch-chroot, install systemd-boot into /boot and create a boot entry

With a little more details:

#2 Create the EFI System Partition

  • gdisk
    • o (create new GPT table)
    • n (create new partition, keep it the first partition and 100 MB big, select EF00 hex code)
    • n (create the other partitions as usual)
    • w (write)
  • format it: mkfs.vfat -F32 /dev/sda1

If you run into the “WARNING: Not enough clusters for a 32 bit FAT!” error, even with the -s2 and -s1 arguments, reboot the system and try again (it worked for me).

#3 Mount /dev/sda2 onto /mnt/boot after mounting /dev/sda1) and run pacstrap; that way, /boot files are already on the UEFI boot partition

mount /dev/sda2 /mnt
mkdir /mnt/boot
mount /dev/sda1 /mnt/boot
pacstrap /mnt base
genfstab -U /mnt >> /mnt/etc/fstab
arch-chroot /mnt

#4 After chroot, install boot loader and create the boot entry

  • install bootloader
bootctl --path=/boot install
  • identify the root partition (not /boot) uuid using ls -l /dev/disk/by-partuuid/
  • create /boot/loader/entries/arch.conf as follows (and update /boot/loader/loader.conf to default to “arch”)
title Arch Linux
linux /vmlinuz-linux
initrd /intel-ucode.img
initrd /initramfs-linux.img
options root=PARTUUID=4f66ed9b-f72d-62c1-89a6-7e2f1979a8f6 rootfstype=ext4 add_efi_memmap

The painful part was to copy-paste the partition uuid in the cmdline environment (you can’t use systemd to run sshd until the installation is complete and you rebooted the system — or i missed something here).

NB: the instructions above are for the archlinux-2016.09.03-dual.iso release.



March 7, 2016 / ftth

Properly cancelling a gobject action

When you use glib’s timeout_add or idle_add (examples below are for python), you can cancel the action before it is run by executing source_remove.

def action():
 return False
tid = gobject.timeout_add(1000, action)

However, if the action was already run, the source_remove will trigger the following warnings in the terminal output:

GLib-CRITICAL **: Source ID XXX was not found when attempting to remove it

The documentation states that “It is a programmer error to attempt to remove a non-existent source.” because “source IDs can be reissued after a source has been destroyed”

If you use gobject to schedule a large number of actions, it means that upon cancelling the actions batch, you will end up with tons of warnings on the terminal for each action that has already been run.

I encountered this issue while developing a python benchmarking script that uses gobject to schedule the execution of simulated users. Before running the mainloop, gobject.timeout_add is used for one-time execution of adding simulated users during the test duration. Every source id is stored inside a list so that upon cancelling, we can batch-cancel them; however, there is no way to tell if a particular action id is still valid, so batch-cancelling is done on all actions (regardless if they have been executed already or not).

A way to fix this (thanks to matplotlib‘s zeroSteiner for the tip) is to get the gobject mainloop context, and check if the gobject action source id is still in the execution queue:

context = ml.get_context()
action = context.find_source_by_id(tid)
if action and not action.is_destroyed():

However, the documentation states that “It is a programmer error to attempt to lookup a non-existent source.”, so maybe that’s not the cleanest way. If you know a better one, please let me know.


January 9, 2016 / ftth

Benchmarking gstreamer OpenGL performance on raspberrypi

After a lot of tinkering (videotestsrc, using temporary gdp files in /tmp), i finally found the optimal way to benchmark the pi gl display performance (of course blocksize needs to be adjusted to a raw buffer size).

gst-launch-1.0 filesrc num-buffers=100 location=/dev/zero blocksize=8294400 ! videoparse format=rgba width=1920 height=1080 ! glimagesink sync=false ... Execution ended after 0:00:09.687275649

Then divide the number of buffers (100) by the execution time (9.69), giving 100/9.69 = ~10 fps.

videotestsrc was quite slow, gdpdepay was killing performance (inducing additional copying), and working with raw files in /tmp was a little bit slower (but still the best way to test pre-rendered samples, e.g. for encoder benchmarking). Using /dev/zero allows to generate completely zeroes buffers very cheaply (meaning completely black and transparent images).


Note that Gstreamer 1.4 (raspbian) and 1.6.2 (arch) have the same performance, and results seem to be the same on Pi B+ and 2.

Just uploading raw 1080p video to the GLES context (without displaying) runs at 23 fps, representing the actual memory speed bottleneck (= 1.5 Gbits/s !)

gst-launch-1.0 filesrc num-buffers=100 location=/dev/zero blocksize=8294400 ! videoparse format=rgba width=1920 height=1080 ! glupload ! fakesink
Execution ended after 0:00:04.234214792

Unfortunately, this means that the RaspberryPi isn’t usable for any project requiring 30 frames per second HD display performance using Gstreamer.




December 11, 2015 / ftth

Compiling glimagesink for GLES (without Xorg) on RaspberryPi

The original RaspberryPi has awesome software support for many things, but when things get to multimedia capabilities, apart from the reference implementations (omxplayer, raspivid…), things tend to get messy or inconsistent, requiring you to recompile heavily patched packages.

As an example, i tried to compile the latest Gstreamer OpenGL elements without Xorg support so that it is possible to use OpenGL without the whole Xorg stack, for e.g. kiosk-style uses. Moreover, the current OpenGL/GLX/Xorg stack on the RaspberryPi is not hardware-accelerated (yet), so using GLES using the vendor SDK should offer better performance.

After a lot of fumbling, here’s a quick summary of the steps required to compile it (most of the time spent was to figure out the CFLAGS and LDFLAGS necessary  to use the SDK OpenGL headers, and complicated by a “bug/feature” with headers within the raspberrypi official sdk and the fact that Mesa libraries can be used at runtime instead of the rpi sdk):

pacman -S gstreamer base-devel
git clone git://
cd gst-plugins-bad
git checkout -b remotes/origin/1.6
./configure CFLAGS="-I/opt/vc/include -I /opt/vc/include/interface/vcos/pthreads -I /opt/vc/include/interface/vmcs_host/linux/" LDFLAGS="-L/opt/vc/lib" --disable-gtk-doc --disable-opengl --enable-gles2 --enable-egl --disable-glx --disable-x11 --disable-wayland --enable-dispmanx --with-gles2-module-name=/opt/vc/lib/ --with-egl-module-name=/opt/vc/lib/

[go grab coffee/lunch/...]

mkdir -p ~/.local/share/gstreamer-1.0/plugins
cp ./ext/gl/.libs/  ~/.local/share/gstreamer-1.0/plugins

Then, after copying the relevant .so files to ~/.local/share/gstreamer-1.0/plugins, you should finally be able to display video using gstreamer:

GST_GL_WINDOW=dispmanx GST_GL_API=gles2 GST_GL_PLATFORM=egl gst-launch-1.0 videotestsrc ! glimagesink

The environment variables are not even be necessary if only a single platform is supported (which is the case here), so you can even run

gst-launch-1.0 videotestsrc ! glimagesink


I also created an AUR package (gst-plugins-bad-rpi-nox) for easier operation — but that will still take a few hours to complete.

Many thanks to Julien Isorce and Matthew Waters for their help !