Re: [RFC PATCH v3 1/3] tracing: Introduce tracepoint extended structure

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On Sat, Oct 26, 2024 at 8:48 AM Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>
> Shrink the struct tracepoint size from 80 bytes to 72 bytes on x86-64 by
> moving the (typically NULL) regfunc/unregfunc pointers to an extended
> structure.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Michael Jeanson <mjeanson@xxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Yonghong Song <yhs@xxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: bpf@xxxxxxxxxxxxxxx
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Jordan Rife <jrife@xxxxxxxxxx>
> ---
>  include/linux/tracepoint-defs.h |  8 ++++++--
>  include/linux/tracepoint.h      | 19 +++++++++++++------
>  kernel/tracepoint.c             |  9 ++++-----
>  3 files changed, 23 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index 60a6e8314d4c..967c08d9da84 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -29,6 +29,11 @@ struct tracepoint_func {
>         int prio;
>  };
>
> +struct tracepoint_ext {
> +       int (*regfunc)(void);
> +       void (*unregfunc)(void);
> +};
> +
>  struct tracepoint {
>         const char *name;               /* Tracepoint name */
>         struct static_key_false key;
> @@ -36,9 +41,8 @@ struct tracepoint {
>         void *static_call_tramp;
>         void *iterator;
>         void *probestub;
> -       int (*regfunc)(void);
> -       void (*unregfunc)(void);
>         struct tracepoint_func __rcu *funcs;
> +       struct tracepoint_ext *ext;
>  };
>
>  #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 0dc67fad706c..83dc24ee8b13 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -302,7 +302,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>   * structures, so we create an array of pointers that will be used for iteration
>   * on the tracepoints.
>   */
> -#define DEFINE_TRACE_FN(_name, _reg, _unreg, proto, args)              \
> +#define __DEFINE_TRACE_EXT(_name, _ext, proto, args)                   \
>         static const char __tpstrtab_##_name[]                          \
>         __section("__tracepoints_strings") = #_name;                    \
>         extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name); \
> @@ -316,9 +316,9 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>                 .static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \
>                 .iterator = &__traceiter_##_name,                       \
>                 .probestub = &__probestub_##_name,                      \
> -               .regfunc = _reg,                                        \
> -               .unregfunc = _unreg,                                    \
> -               .funcs = NULL };                                        \
> +               .funcs = NULL,                                          \
> +               .ext = _ext,                                            \
> +       };                                                              \
>         __TRACEPOINT_ENTRY(_name);                                      \
>         int __traceiter_##_name(void *__data, proto)                    \
>         {                                                               \
> @@ -341,8 +341,15 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>         }                                                               \
>         DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
>
> -#define DEFINE_TRACE(name, proto, args)                \
> -       DEFINE_TRACE_FN(name, NULL, NULL, PARAMS(proto), PARAMS(args));
> +#define DEFINE_TRACE_FN(_name, _reg, _unreg, _proto, _args)            \
> +       struct tracepoint_ext __tracepoint_ext_##_name = {              \

can be static, no?


> +               .regfunc = _reg,                                        \
> +               .unregfunc = _unreg,                                    \
> +       };                                                              \
> +       __DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
> +
> +#define DEFINE_TRACE(_name, _proto, _args)                             \
> +       __DEFINE_TRACE_EXT(_name, NULL, PARAMS(_proto), PARAMS(_args));
>
>  #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)                             \
>         EXPORT_SYMBOL_GPL(__tracepoint_##name);                         \
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 6474e2cf22c9..5658dc92f5b5 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -278,8 +278,8 @@ static int tracepoint_add_func(struct tracepoint *tp,
>         struct tracepoint_func *old, *tp_funcs;
>         int ret;
>
> -       if (tp->regfunc && !static_key_enabled(&tp->key)) {
> -               ret = tp->regfunc();
> +       if (tp->ext && tp->ext->regfunc && !static_key_enabled(&tp->key)) {
> +               ret = tp->ext->regfunc();
>                 if (ret < 0)
>                         return ret;
>         }
> @@ -362,9 +362,8 @@ static int tracepoint_remove_func(struct tracepoint *tp,
>         switch (nr_func_state(tp_funcs)) {
>         case TP_FUNC_0:         /* 1->0 */
>                 /* Removed last function */
> -               if (tp->unregfunc && static_key_enabled(&tp->key))
> -                       tp->unregfunc();
> -
> +               if (tp->ext && tp->ext->unregfunc && static_key_enabled(&tp->key))
> +                       tp->ext->unregfunc();
>                 static_branch_disable(&tp->key);
>                 /* Set iterator static call */
>                 tracepoint_update_call(tp, tp_funcs);
> --
> 2.39.5
>





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