Boot Time Optimization

From Texas Instruments Embedded Processors Wiki

Contents 1 Boot time optimization 1.1 Boot Time 1.2 In short 1.3 Techniques 1.4 Linux Boot Sequence

Boot time optimization

Boot Time

"Boot Time" referred in this page is the time elapsed from "chip coming out of reset" to "Linux Prompt" This page considers under 2 seconds boot time as fast boot

In short

Reuse the existing knowledge. Lot of knowledge is available inside and outside of TI /* provide relevant links here */. Measure and identify boot time spenders. Optimize them. U-boot probably is one of the key areas to target.

Techniques

• Optimize U-Boot
  • Choose the optimal EMIF settings based on NOR used
  • Optimize the NOR to RAM copy
  • Optimize Crc32
  • Avoid printfs
  • Avoid I2C or any other slow peripheral access during U-boot
• Optimize Kernel
  • Remove unused components from Kernel
  • Use loadable modules option to defer initialization of components to after-boot.
    Example: network initialization.
  • Avoid Linux timer calibration loop
  • Avoid Kernel printks
• Optimize Filesystem
  • Rebuild Rootfilesystem with minimal components
  • Use cramfs as rootfilesystem

Linux Boot Sequence

1. ARM boots and starts executing U-boot code from NOR in-place
2. U-boot copies Kernel to RAM
3. U-boot copies filesystem to RAM (copy can be avoided using flash filesystem /* link to relevant page here */ )
4. U-Boot sets parameters and starts Kernel
5. Kernel uncompresses itself
6. Kernel initialization
7. Driver Initialization
8. Init
9. Init scripts
10. Shell

see also:

1. Measuring Boot Time
2. All This For 1 Second Boot

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