linux-kernel - Re: [PATCH -v5 08/11] tracing: not trace mips_timecounter

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Date:	Mon, 2 Nov 2009 22:43:55 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, Thomas Gleixner <tglx@...utronix.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Nicholas Mc Guire <der.herr@...r.at>,
	Richard Sandiford <rdsandiford@...glemail.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Adam Nemet <anemet@...iumnetworks.com>,
	Patrik Kluba <kpajko79@...il.com>
Subject: Re: [PATCH -v5 08/11] tracing: not trace mips_timecounter_init()
	in MIPS

On Mon, Oct 26, 2009 at 05:42:36PM +0800, Wu Zhangjin wrote:
> On Mon, 2009-10-26 at 01:27 +0100, Frederic Weisbecker wrote:
> > 2009/10/25 Wu Zhangjin <wuzhangjin@...il.com>:
> > > -static inline u64 mips_timecounter_read(void)
> > > +static inline u64 notrace mips_timecounter_read(void)
> > 
> > 
> > You don't need to set notrace functions, unless their addresses
> > are referenced somewhere, which unfortunately might happen
> > for some functions but this is rare.
> > 
> 
> Okay, Will remove it.



Oops, a word has escaped from my above sentence. I wanted to say:

"You don't need to set notrace to inline functions" :)


> > Hmm yeah this is not very nice to do that in core functions because
> > of a specific arch problem.
> > At least you have __notrace_funcgraph, this is a notrace
> > that only applies if CONFIG_FUNCTION_GRAPH_TRACER
> > so that it's still traceable by the function tracer in this case.
> > 
> > But I would rather see a __mips_notrace on these two core functions.
> 
> What about this: __arch_notrace? If the arch need this, define it,
> otherwise, ignore it! if only graph tracer need it, define it in "#ifdef
> CONFIG_FUNCTION_GRAPH_TRACER ... #endif".



The problem is that archs may want to disable tracing on different
places.
For example mips wants to disable tracing in timecounter_read_delta,
but another arch may want to disable tracing somewhere else.

We'll then have several unrelated __arch_notrace. One that is relevant
for mips, another that is relevant for arch_foo, but all of them will
apply for all arch that have defined a __arch_notrace.

It's true that __mips_notrace is not very elegant as it looks like
a specific arch annotation intruder.

But at least that gives us a per arch filter granularity.

If only static ftrace could disappear, we could keep only dynamic
ftrace and we would then be able to filter dynamically.
But I'm not sure it's a good idea for archs integration.

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