Kernel Start-up Time

[Caglar Akyuz]

On Tuesday 19 January 2010 11:02:35 am Russell King - ARM Linux wrote:
> On Tue, Jan 19, 2010 at 10:36:21AM +0200, Caglar Akyuz wrote:
> > What I'm looking for is whether early arm boot sequence is 1.3 secs or
> > not. I may be wrong but my guess is before jumping to generic
> > "start_kernel" function following files are executed:
> >
> > * arch/arm/kernel/head.S
> > * arch/arm/kernel/head-common.S
> > * arch/arm/mm/proc-arm926.S
> >
> > And these 3 files cost me 1.3 seconds. Initializing page tables, caches
> > etc costing that much doesn't seem optimal to me. This is what I'm trying
> > to find out.
> 
> Only if your CPU is really inefficient when caches are turned off will
> it take 1.3 seconds.
> 
> Try reading a cycle counter at the start of head.S, save it in memory.
> Read it again in start_kernel() and save it somewhere again, and
> compare the two values.  I think you'll find that it's not this code
> which is taking 1.3 seconds.
> 

Thanks, you were right. This part is only taking 3 milliseconds. It turns out 
that my usage of early printk was wrong.

Caglar