linux-kernel - Re: [PATCH 1/4] tracing: move __DO

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Date:	Fri, 17 Apr 2009 18:23:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 1/4] tracing: move __DO_TRACE out of line


* Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> > > +#define DEFINE_DO_TRACE(name, proto, args)				\
> > > +	void __do_trace_##name(struct tracepoint *tp, TP_PROTO(proto))	\
> > > +	{								\
> > 
> > that needs to be marked notrace, otherwise the function tracer 
> > becomes noisy. (or even lockupy.)
> 
> I guess I'll have to put it more clearly : I am all for minimizing 
> tracepoint header dependency, but I'll be nacking this kind of 
> out-of-lining patch. Taking a function call, and moving it 
> out-of-line (thus duplicating the function call for nothing) seems 
> *really* pointless and will hurt tracer performance.

No need to nak - just say you dont like it and it gets fixed :)

I meant to suggest to Jeremy to measure the effect of this 
out-of-lining, in terms of instruction count in the hotpath.

> If thread_info.h is now so big that it needs a cleanup, I guess 
> we'll just have to do it.

Music to my ears ...

	Ingo
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