Re: Is it possible to use ftrace to measure secondary CPU bootup time

["Huang\, Ying" <ying.huang@intel.com>]

Steven Rostedt <rostedt@goodmis.org> writes:

> On Mon, 24 Jul 2017 13:46:07 +0800
> "Huang\, Ying" <ying.huang@intel.com> wrote:
>
>> Hi, Steven,
>> 
>> We are working on parallelizing secondary CPU bootup.   So we need to
>> measure the bootup time of secondary CPU, that is, measure time spent in
>> smp_init() and its callees.  But we found that ftrace now doesn't
>> support measure time spent in smp_init() because it is called too early
>> (before core_initcall()?).  So, do you think it is possible to use
>> ftrace to measure secondary CPU bootup time?
>
> One could trace with function tracing that early, but that wont give
> you the timings you are looking for. The best it probably could do is
> to look at the function timestamps of what is called after smp_init.
> That is, trace smp_init() and sched_init_smp() and take the difference.
>
> Function graph tracing (which is what you are probably looking for) is
> much more heavy weight than function tracing. It requires some setup
> that isn't ready that early. Although, I'm sure I can work to get it
> there, but it's not trivial.

Got it!  Thanks a lot!

Best Regards,
Huang, Ying

> -- Steve