linux-kernel - Re: [PATCH v3] ftrace: add a tracepoint for __raise_softirq

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Date:	Mon, 11 May 2009 10:27:34 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com,
	zhaolei@...fujitsu.com, laijs@...fujitsu.com,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [PATCH v3] ftrace: add a tracepoint for
	__raise_softirq_irqoff()

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> On Mon, 11 May 2009, Mathieu Desnoyers wrote:
> > 
> > Yes, we should try to fix TRACE_EVENT, but we should fix it _before_ we
> > start using it widely. Circular header dependencies is a real problem
> > with TRACE_EVENT right now.
> > 
> > Until we fix this, I will be tempted to stay with a known-good solution,
> > which is DECLARE/DEFINE_TRACE.
> 
> The majority of tracepoints happen is C files. Those few cases where they 
> are used in headers is where the issues arise.
> 
> But...
> 
> I did not want to uglify all trace event headers with:
> 
> #ifdef CREATE_FOO_TRACE_POINTS
> #undef CREATE_FOO_TRACE_POINTS
> #include <trace/define_trace.h>
> #endif
> 
> We would only need to do that for those trace points that need to be 
> included in header files. Then the declaration C file would need to define 
> both CREATE_FOO_TRACE_POINTS and CREATE_TRACE_POINTS
> 
> #define CREATE_FOO_TRACE_POINTS
> #define CRATE_TRACE_POINTS
> #include <trace/events/foo.h>
> 
> 
> But this is pretty trivial to solve, and I do not consider it a show 
> stopper or a major header dependency problem.
> 
> -- Steve
> 

Hrm, is there any way to solve it elegantly ?

What we really need is to see the cases where TRACE_EVENT() is used as a
declaration vs the case where it expands
TP_STRUCT__entry/TP_fast_assign/TP_printk as having different
dependencies. The problem comes when we bring the include dependencies
of the TP_fast_assign part into the tracepoint header and it becomes
a dependency of the TRACE_EVENT() declaration-only part.

Can we do the following ?

All tracepoint headers could surround the include dependencies by :

#ifdef BUILD_EVENTS
#include <veryannoyingheaderdependency.h>
#endif

And then we follow this by the TRACE_EVENT() declarations.

BUILD_EVENTS would only be defined in kernel/trace/events.c.

I think it should work, but it looks a bit too simple, so I may have
missed something... ?

Mathieu


-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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