How to profile the kernel during its initialization?

[Da Zheng]

On 07/05/11 21:17, Vladimir Murzin wrote:
> On Wed, Jul 6, 2011 at 12:47 AM, Zheng Da<zhengda1936 at gmail.com>  wrote:
>> Hello
>>
>> Can we profile the kernel during its initialization? perf is
>> initialized in an early stage in start_kernel(), but it seems there
>> are no command-line parameters to enable it.
>> Does anyone have any ideas how to profile the kernel during its
>> initialization (before user space programs start to run)? I think
>> someone should have the similar problem as me, and there should be
>> some solutions.
>>
>> Thanks,
>> Da
>>
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>>
> Hi Da,
>
> Have a look at ftrace. It could be used to profile initcalls.
> Just add following boot options:
>
> initcall_debug, ftrace=initcall
>
> More details on
> http://www.omappedia.org/wiki/Installing_and_Using_Ftrace#Boot_Tracer
I'm reading the code of ftrace. Most of tracers are registered in device 
initcalls. So if I enable a tracer in the kernel parameters, it only 
starts to work after device initcalls. Actually, what I really want to 
trace is device initcalls.

Is there any reason why tracers have to be registered in device 
initcalls? Can I move them to an earlier place? at least some of them, 
such as function tracer and function graph tracer.

Thanks,
Da