linux-kernel - Re: [PATCH 2/3] tracing: Move enabling tracepoints to just after mm

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Date:	Sun, 14 Dec 2014 13:20:20 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH 2/3] tracing: Move enabling tracepoints to just after
 mm_init()

On Sun, 14 Dec 2014 10:14:44 -0800
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:


> > diff --git a/init/main.c b/init/main.c
> > index 800a0daede7e..060e60b6aa59 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -561,6 +561,9 @@ asmlinkage __visible void __init start_kernel(void)
> >  	trap_init();
> >  	mm_init();
> > 
> > +	/* trace_printk() and trace points may be used after this */
> > +	trace_init();
> 
> Or if you aren't going to use call_rcu_sched() before this point, I could
> move the call_rcu_sched()-relevant initialization to this point.  Or make
> the compiler do it -- I am pretty sure that the per-CPU variables are in
> place at this point.
> 

Well, we could move trace_init() after rcu_init() for now too, and
remove my tracepoint patch. But I'd like to have trace_init() go before
sched_init() since that could possibly use debugging tracepoints as
well.

So if you could add a rcu_partial_init() that makes calling
call_rcu_sched() work, that would be great. That could be for 3.20
then, and for now, I just move trace_init() after rcu_init() which is
still before irq_init() that Thomas needs for his work.

-- Steve
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