Re: [PATCH v3] ftrace: add a tracepoint for __raise_softirq_irqoff()

Mathieu Desnoyers
2009-05-12T13:14:48Z

* Xiao Guangrong (xiaoguangrong@cn.fujitsu.com) wrote:
>
>
> Mathieu Desnoyers wrote:
> > * Steven Rostedt (rostedt@goodmis.org) wrote:
> >>
> >>
> >> On Mon, 11 May 2009, Mathieu Desnoyers wrote:
> >>
> >>> * Steven Rostedt (rostedt@goodmis.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.
>
> > Yes, but this would solve most of the include dependency problems at
> > once. We would only have dependency on preempt.h left, which alone is
> > easier to deal with. And if headers don't need to include any annoying
> > headers, they don't need to use the ifdef BUILDING_EVENTS. But my point
> > is that when it's needed (and we already see two cases where it's
> > needed, with pvops instrumentation and softirq instrumentation, and I
> > guess we'll see much more), it's good to have this infrastructure in
> > place, so people don't end up trying to do hacks to the kernel code
> > changing inlines for function calls to try to deal with the circular
> > include issue.
> >
> > I think it's
> >
> > a) needed
> > b) it does not hurt anyone who does not need it.
> >
> > So I would definitely recommend adding such define.
> >
>
> Sorry for my poor English.
> Problem is not only in TP_printk, but also in TP_PROTO if we add a
> tracer in header file.
> So, it can't be solved only by "get rid of including ftrace parts"
>
> Take v2 patch for example:
> (it is at: http://marc.info/?l=linux-kernel&m=124081169727739&w=2)
>
> In order to trace __raise_softirq_irqoff(), we should add
> a trace function in __raise_softirq_irqoff() and include
> <include/trace/irq.h> in interrupte.h.
> If we put <include/trace/irq.h> on top of linux/irq.h,
> we will see a warning of "struct softirq_action declared
> inside parameter list" in compile. It is because struct irqaction's
> definition is bypasswd before TP_PROTO.
>

Then add a forward declaration of

struct softirqaction;

At the top of trace/irq.h. I did it in quite a few places in the LTTng
tree. TP_PROTO just needs a forward declaration, not the full structure
declaration.

Only the ftrace-specific parts will need the #include <linux/irq.h>,
which we should put in a #ifdef :

sched.c:
#include linux/interrupt.h
|
|-->include <trace/irq.h>
#ifdef BUILDING_EVENTS
/*
* Includes needed by TP_fast_assign, TP_printk, and
* TP_STRUCT__entry :
*/
# include <linux/interrupt.h>
#else
/* Forward declarations for TP_PROTO */
struct softirq_action;
#endif

TRACE_EVENT(......);
|-->TP_PROTO(int irq, struct irqaction *action),
(but struct softirq_action is not declared before,
it raise a compile warning:struct softirq_action declared
inside parameter list.
|-> ......

Mathieu

>
> I can't see the solvent for this in your discuss or I understand wrong?
>
> Xiao
>
> > Mathieu
> >
> >> -- 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
> >>>
> >

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