linux-kernel - Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context

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Message-ID: <20120905004248.GA12373@jtriplet-mobl1>
Date:	Tue, 4 Sep 2012 17:42:49 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used
 from interrupt context

On Tue, Sep 04, 2012 at 07:46:42PM -0400, Steven Rostedt wrote:
> On Tue, 2012-09-04 at 16:33 -0700, Josh Triplett wrote:
> >  
> > > > +#ifdef MODULE
> > > > +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
> > > > +	static inline void trace_##name##_rcuidle(proto)		\
> > > > +	{								\
> > > > +		if (static_key_false(&__tracepoint_##name.key))		\
> > > > +			__DO_TRACE(&__tracepoint_##name,		\
> > > > +				TP_PROTO(data_proto),			\
> > > > +				TP_ARGS(data_args),			\
> > > > +				TP_CONDITION(cond),			\
> > > > +				rcu_idle_exit(),			\
> > > > +				rcu_idle_enter());			\
> > > > +	}
> > > > +#else
> > > > +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
> > > > +#endif
> > > > +
> > > 
> > > Egad! More macros on top of macros! Yeah I know I'm the most guilty of
> > > this, but it just seems to add one more indirection that I would like to
> > > avoid.
> > 
> > This doesn't seem to add a significant amount of complexity; it forwards
> > exactly the same parameters to the helper macro, and just moves the one
> > function definition there and makes it conditional.  This still seems
> > more preferable than exporting functions just so they won't get called.
> 
> The change itself is not complex. But what is already there is complex
> enough. I'm talking more about adding to:
> 
> $ grep '#define' include/linux/tracepoint.h
> #define _LINUX_TRACEPOINT_H
> #define PARAMS(args...) args
> #define TP_PROTO(args...)       args
> #define TP_ARGS(args...)        args
> #define TP_CONDITION(args...)   args
> #define __DO_TRACE(tp, proto, args, cond, prercu, postrcu)              \
> #define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
> #define DEFINE_TRACE_FN(name, reg, unreg)                                \
> #define DEFINE_TRACE(name)                                              \
> #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)                              \
> #define EXPORT_TRACEPOINT_SYMBOL(name)                                  \
> #define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
> #define DEFINE_TRACE_FN(name, reg, unreg)
> #define DEFINE_TRACE(name)
> #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
> #define EXPORT_TRACEPOINT_SYMBOL(name)
> #define DECLARE_TRACE_NOARGS(name)                                      \
> #define DECLARE_TRACE(name, proto, args)                                \
> #define DECLARE_TRACE_CONDITION(name, proto, args, cond)                \
> #define TRACE_EVENT_FLAGS(event, flag)
> #define DECLARE_EVENT_CLASS(name, proto, args, tstruct, assign, print)
> #define DEFINE_EVENT(template, name, proto, args)               \
> #define DEFINE_EVENT_PRINT(template, name, proto, args, print)  \
> #define DEFINE_EVENT_CONDITION(template, name, proto,           \
> #define TRACE_EVENT(name, proto, args, struct, assign, print)   \
> #define TRACE_EVENT_FN(name, proto, args, struct,               \
> #define TRACE_EVENT_CONDITION(name, proto, args, cond,          \
> #define TRACE_EVENT_FLAGS(event, flag)

Yeah, I've had the adventure of hand-tracing through most of those in
the past myself. :)  At least they have a fairly clear hierarchy,
without particularly complex conditionals.

Ah, for a language with decent code generation facilities. :)

> > I could live with that; it seems preferable to unnecessary exports,
> > though it still seems much uglier to me than the conditional definition
> > of trace_*_rcuidle. :)
> 
> We could add either. Probably keep the ugliness of tracepoints inside
> the tracepoint code than to start spreading it around to rcu. RCU has
> its own ugliness features ;-)
> 
> Hence, I would be OK if you send me a patch that does what you proposed
> and removes the EXPORT from RCU.

To clarify: does what I proposed as in the macro change to avoid
defining trace_*_rcuidle in modules, or makes the change to define panicy
versions of the two functions trace_*_rcuidle needs?

- Josh Triplett
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