From: eLinux.org

DMA Copy Of Kernel On Startup

Contents

• 1 Description
• 2 Rationale
• 3 Resources
  • 3.1 Projects
• 4 Specifications
• 5 Downloads
  • 5.1 Patch
  • 5.2 Utility programs
• 6 How To Use
• 7 Sample Results
  • 7.1 Case Study 1
  • 7.2 Case Study 2
• 8 Status
• 9 Future Work/Action Items

Description

This section describes the technology of DMA copy of kernel on startup.
It’s necessary to copy binary images, such as a kernel image, file
system images, and so on, from ROM to RAM on bootup if XIP isn’t used.
In this case, using DMA transfer is very efficient to save the time and
CPU resources.

Rationale

This feature is important to CELF because it reduces bootup time
significantly.

Resources

Projects

None.

Specifications

None.

Downloads

Patch

Sorry but there is no available patch at this time.

Utility programs

None

How To Use

Sample Results

Case Study 1

Jyunji Kondo (of Fujitsu Prime Software Technologies) measured the
result of using DMA kernel copy on FR-V processor.

Here is the graphic chart which illustrates the elapse time of each
startup stage.

Figure 1: Comparison of normal and fast boot

Hardware
initialization consumes about 200 milliseconds before firmware init.

And here is the table which shows the actual performance number.

In the normal boot case, the kernel image whose size is 1.7MB around is
copied from ROM to RAM by CPU at firmware init. On the other hand, DMA
copy is used in the fast boot case and it reduces about 180
milliseconds.

It owes much to the potentiality of FR-V processor, but it’s worthy of
consideration to use such a hardware assist feature for reducing bootup
time.

Case Study 2

Status

Status - measured
not started, researched, implemented, measured, documented, accepted

• Architecture Support:

  (for each arch, one of: unknown, patches apply, compiles, runs, works,
  accepted)

  • i386: unknown
  • ARM: unknown
  • PPC: unknown
  • MIPS: unknown
  • SH: unknown
  • FR-V: works

Future Work/Action Items

Categories:

• Boot Time
• Bootloader