This page has information about reducing boot-up time for a Linux system. This is of interest for many embedded developers, because for many products customers expect to be able to use them very soon after system startup.
The following are individual pages with information about various technologies relevant to improving boot-up time for Linux. Some of these describe local patches available on this site. Others point to projects or patches maintained elsewhere.
Measuring Boot-up Time
- Printk Times - simple system for showing timing information for each printk.
- Kernel Function Trace - system for reporting function timings in the kernel.
- Linux Trace Toolkit - system for reporting timing data for certain kernel and process events.
Technologies and Techniques for Reducing Boot-up Time
- Disable Console - Avoid overhead of console output during system startup.
- RTC No Sync - Avoid delay to synchronize system time with RTC clock edge on startup.
- Short IDE Delays - Reduce duration of IDE startup delays (this is effective but possibly dangerous).
- Kernel XIP - Allow kernel to be executed in-place in ROM or FLASH.
- IDE No Probe - Force kernel to observe the ide<x>=noprobe option.
- Preset LPJ - Allow the use of a preset loops_per_jiffy value.
- Threaded Device Probing - Allow drivers to probe devices in parallel.
- Application XIP - Allow programs and libraries to be executed in-place in ROM or FLASH
- Pre Linking - Avoid cost of runtime linking on first program load
- Optimize RC Scripts - Reduce overhead of running RC scripts
- DMA Copy Of Kernel On Startup - Copy kernel from Flash to RAM using DMA
- Parallel RC Scripts - Run RC scripts in parallel instead of sequentially
- Application Init Optimizations - Improvements in program load and init time via:
- use of mmap vs. read
- control over page mapping characteristics.
- Boot-up Time Definition Of Terms - definitions of terms used by the CELF Bootup Time working group
- Kernel Instrumentation - lists some known kernel instrumentation tools. These are of interest for measuring kernel startup time.
- Filesystem Information - information about boot-up times with various file systems
- in progress - Boot-up Time Reduction Howto - this is a project to catalog existing boot-up time reduction techniques. Work on this project is under way. The wiki will serve as the primary repository of information gathered for this project.
- no content yet - Boot-up Time Delay Taxonomy - list of delays categorized by boot phase, type and magnitude
- Samsung proof-of-acceptability study for digital still camera: see Linux Boot-Up Time Reduction
- Tim Bird's (Sony) survey of boot-up time reduction techniques:
Additional Projects/Mailing Lists/Resources
- Kexec is a system which allows a system to be rebooted without going through BIOS. That is, a Linux kernel can directly boot into another Linux kernel, without going through firmware. See the white paper at: kexec.pdf
- bootspash.org - technology to put up a splash screen early in boot sequence
- Gentoo Splashscreen - newer technology to put a splash screen early in the boot sequence
- see the HOWTO at: HOWTO FBSplash
- PSplash - PSplash is a userspace graphical boot splash screen for mainly
embedded Linux devices supporting a 16bpp or 32bpp framebuffer.
- FSMLabs Fastboot - press release by FSMLabs about fast booting of their product. Is any of this published?
- Bootchart - a tool for performance analysis and visualization of the Linux boot process. Resource utilization and process information are collected during the user-space portion of the boot process and are later rendered in a PNG, SVG or EPS encoded chart.