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Message-ID: <20100507143901.GA18408@Krystal>
Date: Fri, 7 May 2010 10:39:01 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Lai Jiangshan <laijs@...fujitsu.com>,
Li Zefan <lizf@...fujitsu.com>,
Masami Hiramatsu <mhiramat@...hat.com>,
Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 2/9 - v2][RFC] tracing: Let tracepoints have
data?passed to tracepoint callbacks
* Steven Rostedt (rostedt@...dmis.org) wrote:
>
>
> "Frederic Weisbecker" <fweisbec@...il.com> wrote:
>
> >On Mon, May 03, 2010 at 11:40:47PM -0400, Steven Rostedt wrote:
[...]
> >>
> >> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> >> index 78b4bd3..ee8059a 100644
> >> --- a/include/linux/tracepoint.h
> >> +++ b/include/linux/tracepoint.h
> >> @@ -20,12 +20,17 @@
> >> struct module;
> >> struct tracepoint;
> >>
> >> +struct tracepoint_func {
> >> + void *func;
> >> + void *data;
> >> +};
> >> +
> >> struct tracepoint {
> >> const char *name; /* Tracepoint name */
> >> int state; /* State. */
> >> void (*regfunc)(void);
> >> void (*unregfunc)(void);
> >> - void **funcs;
> >> + struct tracepoint_func *funcs;
> >> } __attribute__((aligned(32))); /*
> >> * Aligned on 32 bytes because it is
> >> * globally visible and gcc happily
> >> @@ -46,14 +51,18 @@ struct tracepoint {
> >> */
> >> #define __DO_TRACE(tp, proto, args) \
> >> do { \
> >> - void **it_func; \
> >> + struct tracepoint_func *it_func_ptr; \
> >> + void *it_func; \
> >> + void *__data; \
> >> \
> >> rcu_read_lock_sched_notrace(); \
> >> - it_func = rcu_dereference_sched((tp)->funcs); \
> >> - if (it_func) { \
> >> + it_func_ptr = rcu_dereference_sched((tp)->funcs); \
> >> + if (it_func_ptr) { \
> >> do { \
> >> - ((void(*)(proto))(*it_func))(args); \
> >> - } while (*(++it_func)); \
> >> + it_func = (it_func_ptr)->func; \
> >> + __data = (it_func_ptr)->data; \
> >> + ((void(*)(proto))(it_func))(args); \
> >
> >
> >So, we had a talk about this and we concluded that it is probably fine
> >on every archs to push one more argument than needed in a function.
> >
>
> Yeah, I'm hoping it's fine.
How about changing the callback prototypes to match the call arguments (changing
the type expected in register/unregister_trace, as well as an additional "check
type" that I proposed for Ftrace) ?
Otherwise, you basically expect here that:
void fct(void *foo, void *bar, etc etc) (N parameters expected)
{
}
called by:
fct(foo, bar, etc etc, foobar) (N + 1 parameters)
will always work.
Can you show me where the C standard says it is safe to do so ?
Thanks,
Mathieu
>
> >But I think it would be nice to add a comment about this. Firstly
> >because this line breaks all the self-explanation of the code, I mean
> >I tried hard to find how the non-data callback case was handled :)
> >Secondly to also to avoid people asking what happens here.
> >
>
> OK I'll add a bit of comments to the macros. So much for my job security ;-)
>
> >
> >
> >
> >> + } while ((++it_func_ptr)->func); \
> >> } \
> >> rcu_read_unlock_sched_notrace(); \
> >> } while (0)
> >> @@ -63,23 +72,47 @@ struct tracepoint {
> >> * not add unwanted padding between the beginning of the section and the
> >> * structure. Force alignment to the same alignment as the section start.
> >> */
> >> -#define DECLARE_TRACE(name, proto, args) \
> >> +#define __DECLARE_TRACE(name, proto, args, data_proto, data_args) \
> >> extern struct tracepoint __tracepoint_##name; \
> >> static inline void trace_##name(proto) \
> >> { \
> >> if (unlikely(__tracepoint_##name.state)) \
> >> __DO_TRACE(&__tracepoint_##name, \
> >> - TP_PROTO(proto), TP_ARGS(args)); \
> >> + TP_PROTO(data_proto), \
> >> + TP_ARGS(data_args)); \
> >> } \
> >> static inline int register_trace_##name(void (*probe)(proto)) \
> >> { \
> >> - return tracepoint_probe_register(#name, (void *)probe); \
> >> + return tracepoint_probe_register(#name, (void *)probe, \
> >> + NULL); \
> >> + } \
> >> + static inline int unregister_trace_##name(void (*probe)(proto)) \
> >> + { \
> >> + return tracepoint_probe_unregister(#name, (void *)probe,\
> >> + NULL); \
> >> } \
> >> - static inline int unregister_trace_##name(void (*probe)(proto)) \
> >> + static inline int \
> >> + register_trace_##name##_data(void (*probe)(data_proto), \
> >> + void *data) \
> >> { \
> >> - return tracepoint_probe_unregister(#name, (void *)probe);\
> >> + return tracepoint_probe_register(#name, (void *)probe, \
> >> + data); \
> >> + } \
> >> + static inline int \
> >> + unregister_trace_##name##_data(void (*probe)(data_proto), \
> >> + void *data) \
> >> + { \
> >> + return tracepoint_probe_unregister(#name, (void *)probe,\
> >> + data); \
> >> }
> >>
> >> +#define DECLARE_TRACE_NOARGS(name) \
> >> + __DECLARE_TRACE(name, void, , void *__data, __data)
> >
> >
> >
> >That too, may be, deserves a small comment :)
>
> OK
>
> >
> >
> >
> >> +
> >> +#define DECLARE_TRACE(name, proto, args) \
> >> + __DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), \
> >> + PARAMS(proto, void *__data), \
> >> + PARAMS(args, __data))
> >>
> >> #define DEFINE_TRACE_FN(name, reg, unreg) \
> >> static const char __tpstrtab_##name[] \
> >> @@ -100,19 +133,37 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
> >> struct tracepoint *end);
> >>
[...]
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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