Linux-ck - ArchWiki

# Linux-ck

From ArchWiki

Related articles

- Repo-ck
- Modprobed-db

## General package details

Linux-ckAUR 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 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

### Package defaults

There are three modifications to the config files:

1. The options that the CK patchset enable/disable.
2. The tickrate is set to 100 Hz (CK's recommendation).
3. The extra CPU types optionally available to compilation thanks to the GCC patch.

All other options are set to the ARCH defaults outlined in the main kernel's config files. Of course users are free to edit them.

The linux-ckAUR package contains an option to switch on the nconfig config editor (see the section below).

### Long-Term Support (LTS) CK releases

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

- linux-lts-ckAUR - 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-ckAUR, nvidia-304xx-ckAUR, nvidia-340xx-ckAUR, and broadcom-wl-ckAUR 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: 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.

Budget Fair Queueing is a disk scheduler which allows each process/thread to be assigned a portion of the disk throughput. Its creator shares the results of many benchmarks (results and video) which show the latency performance improvement.

As of Linux kernel version 4.12, BFQ has been accepted into the mainline kernel. However, it is only available for blk-mq (Multi-Queue Block) so you will have to pass the kernel boot option scsi_mod.use_blk_mq=1 and manually select BFQ by issuing the following for each of your devices:

     echo bfq > /sys/block/sda/queue/scheduler

where sda is the disk in this example.

An alternative method is to create the file 20-block.rules in /etc/udev/rules.d with the below in it:

     ACTION=="add|change", SUBSYSTEM=="block", ATTR{queue/scheduler}="bfq"

This will set BFQ as default during boot for all the disks.

You can also instruct the kernel to use BFQ on a device-by-device basis. For configuration examples see the Improving performance#IO schedulers section.

Note: Setting `elevator=bfq` as kernel parameter doesn't work anymore.

## 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

### 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 Repo-ck section to set up it correctly.

#### The virtualbox-ck-host-modules package (recommended if Linux-ck is built from AUR)

Install the virtualbox-ck-host-modulesAUR package and then install the virtualbox package.

#### Use DKMS (more complicated, recommended for LTS versions)

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

    # pacman -S virtualbox virtualbox-host-dkms
    # dkms install vboxhost/4.3.12

Note: Make sure to substitute the correct version number of virtualbox in the second command. At the time of writing, 4.3.12 is current.

### 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.

## See also

- Kernel patch repository of Con Kolivas
- Con Kolivas' Blog
- Con Kolivas' desktop-centric kernel patchset
- Wikipedia's Con Kovalis page
- Wikipedia's BFS article

Category:

- Kernel