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Message-ID: <CAEf4BzacJd=hMGOGstf3HYc4BbK1Vt9rDkqptcCeE5=R-EqZ5A@mail.gmail.com>
Date: Sun, 27 Oct 2024 18:22:58 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
Michael Jeanson <mjeanson@...icios.com>, Masami Hiramatsu <mhiramat@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>,
"Paul E . McKenney" <paulmck@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>,
bpf@...r.kernel.org, Joel Fernandes <joel@...lfernandes.org>,
Jordan Rife <jrife@...gle.com>
Subject: Re: [RFC PATCH v3 1/3] tracing: Introduce tracepoint extended structure
On Sat, Oct 26, 2024 at 8:48 AM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> 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@...icios.com>
> Cc: Michael Jeanson <mjeanson@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: bpf@...r.kernel.org
> Cc: Joel Fernandes <joel@...lfernandes.org>
> Cc: Jordan Rife <jrife@...gle.com>
> ---
> 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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