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

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Message-ID: <alpine.DEB.2.00.0905111039470.2492@gandalf.stny.rr.com>
Date:	Mon, 11 May 2009 10:53:01 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
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()




On Mon, 11 May 2009, Mathieu Desnoyers wrote:

> * 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.

That file no longer exists. All the events are created with the 
define_trace.h or ftrace.h file.

We could do something like your

#ifdef BUILD_EVENTS /* or better name BUILDING_EVENTS ?? */
#include <allmyannoyingheaders.h>
[...]
#endif

And then have the define_trace.h file add define it. But this again adds 
more annoying CPP commands to all trace_event headers.

-- Steve

> 
> 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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