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

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Date:   Tue, 25 Jul 2017 08:34:51 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        Mengyang Liu <mengyang.liu@...el.com>,
        "Brandt\, Todd E" <todd.e.brandt@...el.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Is it possible to use ftrace to measure secondary CPU bootup time

Steven Rostedt <rostedt@...dmis.org> writes:

> On Mon, 24 Jul 2017 13:46:07 +0800
> "Huang\, Ying" <ying.huang@...el.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