Kernel Start-up Time

Caglar Akyuz caglarakyuz at
Mon Jan 18 03:54:59 EST 2010

On Monday 18 January 2010 10:39:27 am Tonyliu wrote:
> Caglar Akyuz wrote:
> > Hello,
> >
> > While measuring Linux start-up time, I see that printing version string
> > in "start_kernel" takes ~1.3 seconds. I guess this is the time between
> > from "bootloader jumping to uImage" and "printing version string in
> > generic start_kernel code". Relevant part of my boot log is attached.
> >
> > My question: is it normal this 1.3 sec init time? My system is 297 MHZ
> > arm926ej-s with a 162MHZ DDR2 memory.
> It depends on where you start to measure it?
>     Starting from when power is turned on.
>     Starting from when the first instruction executes.
>     Start from the bootloader tries to load the kernel image.
> ...

That number is relative, it is the time passing from u-boot jumping to kernel 
and kernel starting.

> I think this type of mearsurement  makes no much sense to you, since
> normally
> people want to know
>    When the kernel loads userspace or
>     When the first app starts to run.

First application starts in ~4 second. This time consists of:

1) ~1 sec for application start.
2) ~1 sec for userspace init, mouting filesys, etc.
3) ~1 sec for kernel init for drivers and machine specific code
4) ~1 sec for the aforementioned delay.
> These are more meaningful for specific product.

It is number 4 that I'm trying to understand. I think it has the highest 
chance to contribute to end goal. But if it is as expected, then no room for 
optimization there.


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