linux-kernel - Re: [PATCH] tracing/ftrace: stop {irqs,preempt}soff tracers when tracing is stopped

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Message-ID: <20090318085957.GB15416@elte.hu>
Date:	Wed, 18 Mar 2009 09:59:57 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/ftrace: stop {irqs,preempt}soff tracers when
	tracing is stopped


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Tue, Mar 17, 2009 at 05:59:22PM -0400, Steven Rostedt wrote:
> > 
> > On Tue, 17 Mar 2009, Frederic Weisbecker wrote:
> > > > > +	/*
> > > > > +	 * Stop the tracer to avoid a warning subsequent
> > > > > +	 * to buffer flipping failure because tracing_stop()
> > > > > +	 * disables the tr and max buffers, making flipping impossible
> > > > > +	 * in case of parallels max preempt off latencies.
> > > > > +	 */
> > > > > +	trace->stop(tr);
> > > > >  	/* stop the tracing. */
> > > > >  	tracing_stop();
> > > > 
> > > > I'm actually thinking that tracing_stop() should call the current tracer
> > > > "stop" function.
> > > > 
> > > > -- Steve
> > > 
> > > 
> > > Indeed, it could be better.
> > > But I think of a combination of stop() callback call plus
> > > ring buffer disabled because I'm not sure all tracers implement
> > > the stop callback.
> > 
> > Yes, that's what I meant. The tracing_stop should do a few things, and one
> > of them is to call the stop function if it exists.
> > 
> > > 
> > > Should I send a v2 based on the above?
> > 
> > Sure.
> > 
> > -- Steve
> 
> 
> Ingo,
> 
> I tested the call to the start/stop callbacks from tracing_start() 
> and tracing_stop() but it's not possible for now: the sched_switch 
> tracer register/unregister his tracepoints from these callbacks, 
> thus allocate some memory. But tracing_start/stop can be called 
> from atomic.
> 
> I discussed about that with Steven on irc, and for now the v1 
> should be applied as a temporary solution. We plan to simplify 
> later the start/stop callbacks from each tracers that need it.

ok. Steve, could you please pick v1 up?

	Ingo
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