Kernel Start-up Time

[Steve Chen]

On Mon, 2010-01-18 at 10:54 +0200, Caglar Akyuz wrote:
> 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.
> 

Well, "no room for optimization" is a pretty strong statement.  Last
year Monta Vista demo the 1 second boot.

http://mvista.com/press_release_detail.php?fid=news/2009/Ultra-fast-boot.html&d=

I realized that it is a different and faster processor, but I'm pretty
sure there are plenty of places you can trim the boot time.   It is a
matter of time and effort.  You may want to start with the system
requirement to see if 4 seconds is good enough and go from there.

Regards,

Steve