Kernel Start-up Time

Dirk Behme dirk.behme at
Mon Jan 18 14:39:45 EST 2010

On 18.01.2010 16:39, Steve Chen wrote:
> 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.
> 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.


could help you a little.

Best regards


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