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SubjectRe: [PATCH 01/18] trace: Allow <linux/tracepoint.h> to create empty tracepoints
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And I thought I was nasty with the CPP macros ;-)

Added Mathieu to the Cc since he's the one that wrote the original
tracepoint code.


On Tue, 2010-03-23 at 01:32 +0100, Jan Kara wrote:
> If a particular tracer is disabled, there is no need to generate any tracepoint
> code for it. Actually, the inline checks whether tracepoints of the tracer are
> active have non-negligible impact on a code size [1] and thus can in theory
> lead to slowdown. This is undesirable when e.g. BLK_DEV_IO_TRACE should be
> enabled in the production kernel but KMEMTRACE is disabled.
>
> So introduce a macro trickery in <linux/tracepoint.h> so that each tracer can
> define TRACE_CONFIG to CONFIG_MY_TRACER before including linux/tracepoint.h in
> it's events file and that will result in tracepoints becoming empty if
> CONFIG_MY_TRACER is not defined.
>
> [1] As an example: bloat-o-meter mm/slub.o.untraced mm/slub.o.traced
> add/remove: 61/1 grow/shrink: 24/10 up/down: 6366/-737 (5629)
> function old new delta
> deactivate_slab - 592 +592
> show_stat - 380 +380
> trace_kmalloc_node - 265 +265
> trace_kmalloc - 255 +255
> kmem_cache_alloc_node 590 825 +235
> kmem_cache_alloc 542 768 +226
> kfree 566 763 +197
> kmem_cache_free 478 671 +193
> ...
>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Frederic Weisbecker <fweisbec@gmail.com>
> CC: Ingo Molnar <mingo@redhat.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> include/linux/tracepoint.h | 96 +++++++++++++++++++++++++++++++++++--------
> 1 files changed, 78 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index f59604e..1ad17cc 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -37,8 +37,7 @@ struct tracepoint {
>
> #define TP_PROTO(args...) args
> #define TP_ARGS(args...) args
> -
> -#ifdef CONFIG_TRACEPOINTS
> +#define PARAMS(args...) args
>
> /*
> * it_func[0] is never NULL because there is at least one element in the array
> @@ -63,7 +62,7 @@ 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_1(name, proto, args) \
> extern struct tracepoint __tracepoint_##name; \
> static inline void trace_##name(proto) \
> { \
> @@ -81,26 +80,22 @@ struct tracepoint {
> }
>
>
> -#define DEFINE_TRACE_FN(name, reg, unreg) \
> +#define DEFINE_TRACE_FN_1(name, reg, unreg) \
> static const char __tpstrtab_##name[] \
> __attribute__((section("__tracepoints_strings"))) = #name; \
> struct tracepoint __tracepoint_##name \
> __attribute__((section("__tracepoints"), aligned(32))) = \
> { __tpstrtab_##name, 0, reg, unreg, NULL }
>
> -#define DEFINE_TRACE(name) \
> +#define DEFINE_TRACE_1(name) \
> DEFINE_TRACE_FN(name, NULL, NULL);
>
> -#define EXPORT_TRACEPOINT_SYMBOL_GPL(name) \
> +#define EXPORT_TRACEPOINT_SYMBOL_GPL_1(name) \
> EXPORT_SYMBOL_GPL(__tracepoint_##name)
> -#define EXPORT_TRACEPOINT_SYMBOL(name) \
> +#define EXPORT_TRACEPOINT_SYMBOL_1(name) \
> EXPORT_SYMBOL(__tracepoint_##name)
>
> -extern void tracepoint_update_probe_range(struct tracepoint *begin,
> - struct tracepoint *end);
> -
> -#else /* !CONFIG_TRACEPOINTS */
> -#define DECLARE_TRACE(name, proto, args) \
> +#define DECLARE_TRACE_0(name, proto, args) \
> static inline void _do_trace_##name(struct tracepoint *tp, proto) \
> { } \
> static inline void trace_##name(proto) \
> @@ -114,10 +109,51 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
> return -ENOSYS; \
> }
>
> -#define DEFINE_TRACE_FN(name, reg, unreg)
> -#define DEFINE_TRACE(name)
> -#define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
> -#define EXPORT_TRACEPOINT_SYMBOL(name)
> +#define DEFINE_TRACE_FN_0(name, reg, unreg)
> +#define DEFINE_TRACE_0(name)
> +#define EXPORT_TRACEPOINT_SYMBOL_GPL_0(name)
> +#define EXPORT_TRACEPOINT_SYMBOL_0(name)
> +
> +/*
> + * Below two-level macro magic is really needed to propely expand TRACE_CONFIG
> + * macro to 0 or 1 in the end

This is a really lame comment. There should be almost as much comments
as code when doing CPP trickery like this.

> + */
> +#define __DECLARE_TRACE(config, name, proto, args) \
> + DECLARE_TRACE_##config(name, PARAMS(proto), PARAMS(args))
> +#define __DEFINE_TRACE_FN(config, name, reg, unreg) \
> + DEFINE_TRACE_FN_##config(name, reg, unreg)
> +#define __DEFINE_TRACE(config, name) DEFINE_TRACE_##config(name)
> +#define __EXPORT_TRACEPOINT_SYMBOL_GPL(config, name) \
> + EXPORT_TRACEPOINT_SYMBOL_GPL_##config(name)
> +#define __EXPORT_TRACEPOINT_SYMBOL(config, name) \
> + EXPORT_TRACEPOINT_SYMBOL_##config(name)
> +
> +#define _DECLARE_TRACE(config, name, proto, args) \
> + __DECLARE_TRACE(config, name, PARAMS(proto), PARAMS(args))
> +#define _DEFINE_TRACE_FN(config, name, reg, unreg) \
> + __DEFINE_TRACE_FN(config, name, reg, unreg)
> +#define _DEFINE_TRACE(config, name) __DEFINE_TRACE(config, name)
> +#define _EXPORT_TRACEPOINT_SYMBOL_GPL(config, name) \
> + __EXPORT_TRACEPOINT_SYMBOL_GPL(config, name)
> +#define _EXPORT_TRACEPOINT_SYMBOL(config, name) \
> + __EXPORT_TRACEPOINT_SYMBOL(config, name)
> +
> +#define DECLARE_TRACE(name, proto, args) \
> + _DECLARE_TRACE(TRACE_CONFIG, name, PARAMS(proto), PARAMS(args))
> +#define DEFINE_TRACE_FN(name, reg, unreg) \
> + _DEFINE_TRACE_FN(TRACE_CONFIG, name, reg, unreg)
> +#define DEFINE_TRACE(name) _DEFINE_TRACE(TRACE_CONFIG, name)
> +#define EXPORT_TRACEPOINT_SYMBOL_GPL(name) \
> + _EXPORT_TRACEPOINT_SYMBOL_GPL(TRACE_CONFIG, name)
> +#define EXPORT_TRACEPOINT_SYMBOL(name) \
> + _EXPORT_TRACEPOINT_SYMBOL(TRACE_CONFIG, name)
> +
> +#ifdef CONFIG_TRACEPOINTS
> +
> +extern void tracepoint_update_probe_range(struct tracepoint *begin,
> + struct tracepoint *end);
> +
> +#else /* ! CONFIG_TRACEPOINTS */
>
> static inline void tracepoint_update_probe_range(struct tracepoint *begin,
> struct tracepoint *end)
> @@ -163,11 +199,35 @@ static inline void tracepoint_synchronize_unregister(void)
> synchronize_sched();
> }
>
> -#define PARAMS(args...) args
> -
> #endif /* _LINUX_TRACEPOINT_H */
>
> /*
> + * The two chunks below are out of include file ifdef protection because
> + * we want to be able to define TRACE_CONFIG even before second or even
> + * later include of linux/tracepoint.h.
> + */
> +/*
> + * Make tracepoints which are not converted to a new method of enabling
> + * always compiled in
> + */
> +#ifndef TRACE_CONFIG
> +#define TRACE_CONFIG 1
> +#endif

Hmm, We can have tracepoints in a header. Would this still work if a
header with a tracepoint was not converted but it was included in a file
that was. Of course I haven't seen the other patches yet so I don't yet
know what a conversion looks like.

-- Steve

<
> +
> +/*
> + * If TRACE_CONFIG is defined but a config option it is defined to isn't, make
> + * the result 0. It would require much less magic if the kernel was not
> + * compiled with -Wundef.
> + */
> +#define CONFIG_TEST_1
> +#define _CONFIG_UNDEF(x) !defined(CONFIG_TEST_##x)
> +#define CONFIG_UNDEF(x) _CONFIG_UNDEF(x)
> +#if CONFIG_UNDEF(TRACE_CONFIG)
> +#undef TRACE_CONFIG
> +#define TRACE_CONFIG 0
> +#endif
> +
> +/*
> * Note: we keep the TRACE_EVENT outside the include file ifdef protection.
> * This is due to the way trace events work. If a file includes two
> * trace event headers under one "CREATE_TRACE_POINTS" the first include




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