linux-kernel - Re: sys_sched_yield keeps locked irq before call of schedule()

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Date:	Thu, 6 Nov 2008 09:46:57 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: sys_sched_yield keeps locked irq before call of schedule()


On Thu, 6 Nov 2008, Ingo Molnar wrote:
> > 
> > Quick note. Currently ftrace_printk only shows up if it is set in the 
> > iter_ctrl.
> > 
> >   echo trace_printk > /debug/tracing/iter_ctrl
> > 
> > I'll send out a patch to have it on by default.
> 
> ok, agreed - but in that case please make the NOP tracer 
> tracing_enabled=0 by default. (we'll get a lot of ftrace_printk 
> tracepoints by default otherwise)

Hmm, I think it may be good to leave it on even for the nop tracer.

ftrace_printk's should not be out in open code unless someone is actually 
debugging it. You can use ftrace_printk inside a tracer to write stuff, 
but that printk should be protected somehow by the encompassing tracer.

i.e.

	some_tracer(void) {
		if (!tracer_enabled)
			return;
		ftrace_printk("my special stuff\n");
	}

I would think if someone is debugging their code by using ftrace_printk, 
they probably want it to show up right away, without having to remember to 
do a...


	echo trace_printk > /debug/tracing/iter_ctrl

And still have it show up in the nop tracer.

-- Steve

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