Gamemode

GameMode

GameMode is a daemon/lib combo for Linux that allows games to request a set of optimisations be temporarily applied to the host OS.

The design has a clear-cut abstraction between the host daemon and library (gamemoded and libgamemode), and the client loaders (libgamemodeauto and gamemode_client.h) that allows for safe use without worrying about whether the daemon is installed or running. This design also means that while the host library currently relies on systemd for exchanging messages with the daemon, it's entirely possible to implement other internals that still work with the same clients.

GameMode was designed primarily as a stop-gap solution to problems with the Intel and AMD CPU powersave or ondemand governors, but is now able to launch custom user defined plugins, and is intended to be expanded further, as there are a wealth of automation tasks one might want to apply.

GameMode can leverage support for soft real time mode if the running kernel supports SCHED_ISO. This adjusts the scheduling of the game to real time without sacrificing system stability by starving other processes.

GameMode adjusts the nice priority of games to -4 by default to give it a slight IO and CPU priority over other background processes. This only works if your user is permitted to adjust priorities within the limits configured by PAM. See /etc/security/limits.conf.

Please take note that some games may actually run seemingly slower with SCHED_ISO if the game makes use of busy looping while interacting with the graphic driver. The same may happen if you apply too strong nice values. This effect is called priority inversion: Due to the high priority given to busy loops, there may be too few resources left for the graphics driver. Thus, sane defaults were chosen to not expose this effect on most systems. Part of this default is a heuristic which automatically turns off SCHED_ISO if GameMode detects three or less CPU cores. Your experience may change based on using GL threaded optimizations, CPU core binding (taskset), the graphic driver, or different CPU architectures. If you experience bad input latency or inconsistent FPS, try switching these configurations on or off first and report back. SCHED_ISO comes with a protection against this effect by falling back to normal scheduling as soon as the SCHED_ISO process uses more than 70% avarage across all CPU cores. This default value can be adjusted outside of the scope of GameMode (it's in /proc/sys/kernel/iso_cpu). This value also protects against compromising system stability, do not set it to 100% as this would turn the game into a full real time process, thus potentially starving all other OS components from CPU resources.

GameMode can adjust the io priority of games to benefit from reduced lag and latency when a game has to load assets on demand.

Issues with GameMode should be reported here in the issues section, and not reported to Feral directly.

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Building and installing

If your distribution already has GameMode packaged, it is preferable to install it directly from there. There are Solus, AUR, Gentoo and Fedora packages already available.

GameMode depends on meson for building and systemd for internal communication. This repo contains a bootstrap.sh script to allow for quick install to the user bus, but check meson_options.txt for custom settings.

Ubuntu/Debian (you may also need dbus-user-session)

apt install meson libsystemd-dev pkg-config ninja-build git

Arch

pacman -S meson systemd git

Fedora

dnf install meson systemd-devel pkg-config git

Gentoo

Gentoo has a bleeding-edge ebuild which builds from sources. It will also pull in all the dependencies so you can work on the source code.

ACCEPT_KEYWORDS="**" emerge --ask ~games-util/gamemode-9999

Then clone, build and install a release version of GameMode at 1.2:

git clone https://github.com/FeralInteractive/gamemode.git
cd gamemode
git checkout 1.2
./bootstrap.sh

To build the master branch:

git clone https://github.com/FeralInteractive/gamemode.git
cd gamemode
git submodule update --init --recursive
./bootstrap.sh

This will also satisfy the build requirement inih by pulling it in as a git submodule.

To uninstall:

systemctl --user stop gamemoded.service
cd build/
ninja uninstall

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Requesting GameMode

Users

After installing libgamemodeauto.so.0 simply preload it into the game:

LD_PRELOAD=/usr/\$LIB/libgamemodeauto.so.0 ./game

Or edit the steam launch options:

LD_PRELOAD=$LD_PRELOAD:/usr/\$LIB/libgamemodeauto.so.0 %command%

Please note the backslash here in \$LIB is required.

Developers

Developers can build the request directly into an app. Note that none of these client methods force your users to have the daemon installed or running - they will safely no-op if the host is missing.

// Manually with error checking
#include "gamemode_client.h"

	if( gamemode_request_start() < 0 ) {
		fprintf( stderr, "gamemode request failed: %s\n", gamemode_error_string() );
	}

	/* run game... */

	gamemode_request_end(); // Not required, gamemoded can clean up after game exits

// Automatically on program start and finish
#define GAMEMODE_AUTO
#include "gamemode_client.h"

Or, distribute libgamemodeauto.so and either add -lgamemodeauto to your linker arguments, or add it to an LD_PRELOAD in a launch script.

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Components

gamemoded runs in the background, activates game mode on request, refcounts and also checks caller PID lifetime. Run man gamemoded for command line options.

libgamemode is an internal library used to dispatch requests to the daemon. Note: libgamemode should never be linked with directly.

libgamemodeauto is a simple dynamic library that automatically requests game mode when loaded. Useful to LD_PRELOAD into any game as needed.

gamemode_client.h is as single header lib that lets a game request game mode and handle errors.

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Configuration

The daemon can currently be configured using a gamemode.ini file. gamemode.ini is an example of what this file would look like, with explanations for all the variables.

Config files are loaded and merged from the following directories, in order:

1. /usr/share/gamemode/
2. /etc/
3. $XDG_CONFIG_HOME or $HOME/.config/
4. $PWD

The file parsing uses inih.

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For those with overclocked CPUs

If you have an AMD CPU and have disabled Cool'n'Quiet, or you have an Intel CPU and have disabled SpeedStep, then GameMode's governor settings will not work, as your CPU is not running with a governor. You are already getting maximum performance.

If you are unsure, bootstrap.sh will warn you if your system lacks CPU governor control.

Scripts and other features will still work.

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Contributions

Pull Requests

Pull requests must match with the coding style found in the .clang-format file, please run this before committing:

clang-format -i $(find . -name '*.[ch]' -not -path "*subprojects/*")

Planned Features

• Additional mode-switch plugins
• Improved client state tracking (PID is unreliable)

Maintained by

Feral Interactive

See the contributors section for an extended list of contributors.

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License

Copyright © 2018 Feral Interactive

GameMode is available under the terms of the BSD 3-Clause License (Revised)