Kernel Start-up Time

[Russell King - ARM Linux]

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.