linux-kernel - Re: [PATCH 2/7][RFC] powerpc64: port of the function graph tracer

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Date:	Thu, 12 Feb 2009 23:18:56 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linuxppc-dev@...abs.org, Paul Mackerras <paulus@...ba.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/7][RFC] powerpc64: port of the function graph tracer

On Fri, 13 Feb 2009, Benjamin Herrenschmidt wrote:

> > On Wed, 2009-02-11 at 20:10 -0500, Steven Rostedt wrote:
> > 
> > +# timers used by tracing
> > +CFLAGS_REMOVE_time.o = -pg -mno-sched-epilog
> >  endif
> 
> That means no tracing of the timer interrupts etc... maybe we should
> just move the specific function that we don't want traced out to a
> separate file ? 

The function graph tracer calls cpu_clock, which calls sched_clock, 
to get the times. There's no protection against recursion here, since
we want to let interrupts still be recorded, and we do not need to disable
interrupts.

But if the cpu_clock calls something that is traced, it will recurse, and 
cause a lockup. What ever functions those are, we could annotate with
notrace. I just used the x86 blind method of 'dont trace this file'.

> 
> Appart from that, it looks ok, though I might have missed something :-)

Thanks,

-- Steve

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