Linux-ck

Related articles

• Unofficial user repositories/Repo-ck
• Modprobed-db

General package details

Linux-ck^AUR is a package available both in AUR and in the unofficial repo-ck repository that allows users to run a kernel and headers setup patched with Con Kolivas' ck patchset[1], including a CPU scheduler named MuQSS (Multiple Queue Skiplist Scheduler, pronounced mux) which replaces Brain Fuck Scheduler (BFS), his previous work. Many Arch Linux users choose this kernel for its excellent desktop interactivity and responsiveness under any load situation.

CK patchset is designed for desktop/laptop use but not for servers. It provides low latency environment and works well for 16 CPUs or fewer.

Release cycle

Linux-ck roughly follows the release cycle of the official Arch kernel but not only. The following are requirements for a new package release:

• CK patchset compatible with the current kernel version
• corresponding Arch kernel must be in existence otherwise it will break other packages i.e. nvidia. See git.archlinux.org for the official linux package

Long-Term Support (LTS) CK releases

In addition to the linux-ck^AUR package, there are LTS kernel releases patched with the above patchsets as well and with the previously mentioned modifications:

• linux-lts-ck^AUR - The current Arch Linux LTS kernel patched with the CK patchset

Note: This package is maintained by vishwin, thus pre-compiled versions will not be present in the unofficial ck repo.

Installation options

Note: As with any additional kernel, users need to manually update their boot loader's configuration file in order to make it aware of the new kernel image.

Users have two options to get these kernel packages.

Compile the package from source

The AUR contains entries for both packages mentioned above.

Users can further customize the linux-ck package via tweaks contained in the PKGBUILD:

• Optional nconfig for user specific tweaking.
• Option to compile a minimal set of modules via a make localmodconfig.
• Option to bypass the standard Arch config options and simply use the current kernel configuration file.
• Optionally set the BFQ I/O scheduler as default.

More details about these options are provided in the PKGBUILD itself. Be sure to read them carefully if compiling from AUR!

Note: There are the related PKGBUILDs in AUR for other common kernel modules. For example nvidia-ck^AUR, nvidia-340xx-ck^AUR, and broadcom-wl-ck^AUR to name a few. Alternatively, use the corresponding DKMS package, for instance install nvidia-dkms as described in NVIDIA#Custom kernel.

Use pre-compiled packages

If user prefers to spend no time to compile on their own, the unofficial repo maintained by graysky is available to the community. For details, see: Unofficial user repositories/Repo-ck.

How to enable the BFQ I/O Scheduler

Note: Do not confuse MuQSS (Multiple Queue Skiplist Scheduler) with BFQ (Budget Fair Queueing). MuQSS is a CPU scheduler and is enabled by default whereas BFQ is an I/O scheduler and must explicitly be enabled in order to use it.

See the Improving performance#Input/output schedulers section for some background about the different IO schedulers and how to activate BFQ.

More about MuQSS

See the LKML announcement posted by CK.

Check if MuQSS is enabled

This start-up message should appear in the kernel ring buffer when MuQSS in enabled:

$ dmesg | grep -i muqss
...
MuQSS CPU scheduler v0.120 by Con Kolivas.

MuQSS patched kernels and systemd

It is a common mistake to think that MuQSS does not support cgroups. It does but not all the cgroup features (e.g. CPU limiting will not work).

Troubleshooting

Silencing psi: task underflow message

New in MuQSS v0.185 is support for PSI which CK is characterizing as "completely untested and probably broken."

In response to this, some users may notice psi: task underflow! in dmesg/journalctl output. With the release of 4.20.0-3-ck1, is compiled in but disabled by default. Users wanting PSI enabled should boot with the following [Kernel_parameter] on their respective bootloader config: psi=1

Running VirtualBox with Linux-ck

VirtualBox works just fine with custom kernels such as Linux-ck without the need to keep any of the official Arch kernel headers package on the system.

Do not forget to add users to the vboxusers group:

# gpasswd -a USERNAME vboxusers

Use the unofficial repo (recommended if Linux-ck is installed from Repo-ck)

Note: As of 17-Oct-2012, Repo-ck users can enjoy these modules as pre-compiled packages in the repo itself. If you build Linux-ck from AUR you can not use the repo as all packages in the repo are matched groups.

See the Unofficial user repositories/Repo-ck to set up it correctly.

DKMS

Install virtualbox with the virtualbox-host-dkms package. Then setup DKMS as follows:

# pacman -S virtualbox virtualbox-host-dkms

CPUACCT missing in docker

In newer versions of Linux-ck (some experienced with 4.19, 4.20 seems general), a change to the MuQSS was made that disables the CONFIG_CGROUP_CPUACCT option from the kernel, which makes some usage of docker (run or build) to produce the following error:

$ docker run --rm hello-world

docker: Error response from daemon: unable to find "cpuacct" in controller set: unknown.

This error does not seems to affect the docker daemon, just containers. This is due a change where the CONFIG_CGROUP_CPUACCT kernel option is incompatible with SCHED_MUQSS when the last is set to Y, as seen in a recent commit in ck's repository:

@@ -896,6 +913,7 @@ config CGROUP_DEVICE

 config CGROUP_CPUACCT
        bool "Simple CPU accounting controller"
+       depends on !SCHED_MUQSS
        help
          Provides a simple controller for monitoring the
          total CPU consumed by the tasks in a cgroup.

You can check more information in the forums or in ck's blog.

Downgrading

Users wishing to downgrade to a previous version of Linux-ck, have several options:

• Source archives are available dating back to linux-ck-3.3.7-1.
• AUR.git holds AUR git commits for Linux-ck, dating back to linux-ck-2.6.39.3-1.

Forum support

Always feel free to open a thread in the forums for support purpose. Be sure to give the thread a descriptive title to draw attention to the fact that the post relates to the Linux-ck package.

There is also an official thread for Linux-ck.

See also

• Kernel patch repository of Con Kolivas
• Con Kolivas' Blog
• Con Kolivas' first BFS announcement on the Linux Kernel Mailing List
• Wikipedia's Con Kolivas page
• Wikipedia's BFS article