Difference between revisions of "Linux-ck"

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(A Little About the BFS)
(How to Enable the BFQ I/O Scheduler)
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== How to Enable the BFQ I/O Scheduler ==
== How to Enable the BFQ I/O Scheduler ==
BFQ (Budget Fair Queueing) is a disk scheduler which allows each process/thread to be assigned a portion of the disk throughput.
Budget Fair Queueing is a disk scheduler which allows each process/thread to be assigned a portion of the disk throughput.
=== Globally (for all devices) ===
=== Globally (for all devices) ===

Revision as of 16:49, 13 January 2013

Summary help replacing me

Linux-ck and headers

  • Current version: 3.7.2-2
  • BFS CPU scheduler: v0.426
  • CK Patchset: 3.7-ck1
  • Release date: 12-Jan-2013
Linux-ck/Changelog - Linux-ck Changelog.
Repo-ck - Setup and contents of unofficial repo-ck.
Modprobed_db - Util to keep track of all probed modules.

General Package Details

Linux-ckAUR is a package available in the AUR and in the unofficial linux-ck repo that allows users to run a kernel/headers setup patched with Con Kolivas' ck1 patchset, including the Brain Fuck Scheduler (BFS). Many Archers elect to use this package for the BFS' excellent desktop interactivity and responsiveness under any load situation. Additionally, the bfs imparts performance gains beyond interactivity. For example, see: [CPU_Schedulers_Compared.pdf].

Release Cycle

Linux-ck roughly follows the release cycle of the official ARCH kernel. The following are requirements for its release:

  • Upstream code
  • CK's Patchset
  • BFQ Patchset
  • ARCH config/config.x86_64 sets for major version jumps only

Package Defaults

There are three modifications to the config files:

  1. The options that the ck patchset enable/disable.
  2. The options that the BFQ patchset need to compile without user interaction.
  3. Apply GCC patch that enables additional CPU optimizations at compile time (these options are not part of the standard linux-ck package and are only available when the user compiles custom options).

All other options are set to the ARCH defaults outlined in the main kernel's config files. Users are of course free to modify them! The linux-ck package contains an option to switch on the nconfig config editor (see section below). For some suggestions, see CK's BFS configuration FAQ.

Installation Options

Note: As with *any* additional kernel, users will need to manually edit their boot loader's config file to make it aware of the new kernel images. For example, users of GRUB should execute "grub-mkconfig -o /boot/grub/grub.cfg". Syslinux, GRUB-legacy, etc. will need to be modified as well.

Users have two options to get these kernel packages.

1. Compile the Package From Source

The AUR contains entries for both packages mentioned above.

Users can customize the linux-ck package via tweaks 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's .config file.
  • Optionally set the BFQ I/O scheduler as default.

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

Note: There are related PKGBUILDs in the AUR for other common modules unique to linux-ck. For example nvidia-ckAUR, nvidia-304xx-ckAUR,lirc-ckAUR, and broadcom-wl-ckAUR.

2. Use Pre-Compiled Packages

If users would rather not spend the time to compile on their own, an unofficial repo maintained by graysky is available to the community.

For details, see: Repo-ck.

How to Enable the BFQ I/O Scheduler

Budget Fair Queueing is a disk scheduler which allows each process/thread to be assigned a portion of the disk throughput.

Globally (for all devices)

If compiling from the AUR, simply set the BFQ flag to yes in the PKGBUILD prior to building.


If using the repo packages, append "elevator=bfq" to the kernel boot line in /boot/grub/menu.lst if using grub or in /etc/default/grub under the GRUB_CMDLINE_LINUX_DEFAULT="quiet" line followed by rebuilding /boot/grub/grub.cfg via the standard "grub-mkconfig -o /boot/grub/grub.cfg" command.

Selectively (for only specified devices)

An alternative method is to direct the kernel to use it on a device-by-device basis. For example, to enable it for /dev/sda simply:

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

To confirm, simply cat the same file:

# cat /sys/block/sda/queue/scheduler
noop deadline cfq [bfq] 

Note that doing it this way will not survive a reboot. To make the change automatically at the next system boot, place lines in /etc/tmpfiles.d/IO_scheduler.conf:

w /sys/block/sda/queue/scheduler - - - - bfq


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 packages on the system!

Don't forget to add users to the vboxusers group:

# gpasswd -a USERNAME vboxusers

Option 1. Use the Unofficial Repo (Recommended)

Note: As of 17-Oct-2012, Repo-ck users can enjoy these modules as precompiled packages in the repo itself. If you built your linux-ck from the AUR you CANNOT USE THE REPO as all packages in the repo are matched groups.

See the Repo-ck article to setup http://repo-ck.com for pacman to use directly.

Option 2. The virtualbox-ck-modules package (Recommended if Linux-ck is Built by You from the AUR)

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

Option 3. Use DKMS (More complicated)

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

# pacman -S virtualbox virtualbox-host-dkms
# dkms install vboxhost/4.2.6
Note: Make sure to substitute the correct version number of virtualbox in the second command. At the time of writting, 4.2.6 is current.


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-

Forum Support

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

A Little About the BFS

The Brain Fuck Scheduler is a desktop orientated cpu process scheduler with extremely low latencies for excellent interactivity within normal load levels.

BFS Design Goals

The BFS has two major design goals:

  1. Achieve excellent desktop interactivity and responsiveness without heuristics and tuning knobs that are difficult to understand, impossible to model and predict the effect of, and when tuned to one workload cause massive detriment to another.
  2. Completely do away with the complex designs of the past for the cpu process scheduler and instead implement one that is very simple in basic design.

For additional information, see the linux-ck#Further_Reading_on_BFS_and_CK_Patchset section of this article.

An Example Video About Queuing Theory

See this video about queuing theory for an interesting parallel with supermarket checkouts. Quote from CK, "the relevance of that video is that BFS uses a single queue, whereas the mainline Linux kernel uses a multiple queue design. The people are tasks, and the checkouts are CPUs. Of course there's a lot more to a CPU scheduler than just the queue design, but I thought this video was very relevant."

Some Performance-Based Metrics: BFS vs. CFS

A major benefit of using the BFS is increased responsiveness. The benefits however, are not limited to desktop feel. Graysky put together some non-responsiveness based benchmarks to compare it to the CFS contained in the "stock" linux kernel. Seven different machines were used to see if differences exist and, to what degree they scale using performance based metrics. Again, these end-points were never factors in the primary design goals of the bfs. Results were encouraging.

For those not wanting to see the full report, here is the conclusion: Kernels patched with the ck1 patch set including the bfs outperformed the vanilla kernel using the cfs at nearly all the performance-based benchmarks tested. Further study with a larger test set could be conducted, but based on the small test set of 7 PCs evaluated, these increases in process queuing, efficiency/speed are, on the whole, independent of CPU type (mono, dual, quad, hyperthreaded, etc.), CPU architecture (32-bit and 64-bit), 64 bit) and of CPU multiplicity (mono or dual socket).

Moreover, several "modern" CPUs (Intel C2D and Ci7) that represent common workstations and laptops, consistently outperformed the cfs in the vanilla kernel at all benchmarks. Efficiency and speed gains were small to moderate.

[CPU_Schedulers_Compared.pdf] is available for download.

Check if Enabled

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

# dmesg | grep scheduler
[    0.380500] BFS CPU scheduler v0.420 by Con Kolivas.

BFS Myths

BFS patched kernels CAN in fact use systemd

It is a common mistake to think that bfs does not support cgroups. It does support cgroups, just not all the cgroup features. Systemd works perfectly fine with BFS patched kernels.

Further Reading on BFS and CK Patchset

Linux-ck Package Changelog