linux-kernel - Re: [PATCH v2 25/40] tracing: Add support for dynamic tracepoints

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Date:   Tue, 05 Sep 2017 21:35:12 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        vedang patel <vedang.patel@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        joel opensrc <joel.opensrc@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        baohong liu <baohong.liu@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v2 25/40] tracing: Add support for dynamic tracepoints

Hi Mathieu,

On Tue, 2017-09-05 at 23:29 +0000, Mathieu Desnoyers wrote:
> ----- On Sep 5, 2017, at 5:57 PM, Tom Zanussi tom.zanussi@...ux.intel.com wrote:
> 
> > The tracepoint infrastructure assumes statically-defined tracepoints
> > and uses static_keys for tracepoint enablement.  In order to define
> > tracepoints on the fly, we need to have a dynamic counterpart.
> > 
> > Add a 'dynamic' flag to struct tracepoint along with accompanying
> > logic for this purpose.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > ---
> > include/linux/tracepoint-defs.h |  1 +
> > kernel/tracepoint.c             | 18 +++++++++++++-----
> > 2 files changed, 14 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> > index a031920..bc22d54 100644
> > --- a/include/linux/tracepoint-defs.h
> > +++ b/include/linux/tracepoint-defs.h
> > @@ -32,6 +32,7 @@ struct tracepoint {
> > 	int (*regfunc)(void);
> > 	void (*unregfunc)(void);
> > 	struct tracepoint_func __rcu *funcs;
> > +	bool dynamic;
> > };
> > 
> > #endif
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index 685c50a..1c5957f 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
> > @@ -197,7 +197,9 @@ static int tracepoint_add_func(struct tracepoint *tp,
> > 	struct tracepoint_func *old, *tp_funcs;
> > 	int ret;
> > 
> > -	if (tp->regfunc && !static_key_enabled(&tp->key)) {
> > +	if (tp->regfunc &&
> > +	    ((tp->dynamic && !(atomic_read(&tp->key.enabled) > 0)) ||
> > +	     !static_key_enabled(&tp->key))) {
> > 		ret = tp->regfunc();
> > 		if (ret < 0)
> > 			return ret;
> > @@ -219,7 +221,9 @@ static int tracepoint_add_func(struct tracepoint *tp,
> > 	 * is used.
> > 	 */
> > 	rcu_assign_pointer(tp->funcs, tp_funcs);
> > -	if (!static_key_enabled(&tp->key))
> > +	if (tp->dynamic && !(atomic_read(&tp->key.enabled) > 0))
> > +		atomic_inc(&tp->key.enabled);
> > +	else if (!tp->dynamic && !static_key_enabled(&tp->key))
> > 		static_key_slow_inc(&tp->key);
> > 	release_probes(old);
> > 	return 0;
> > @@ -246,10 +250,14 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> > 
> > 	if (!tp_funcs) {
> > 		/* Removed last function */
> > -		if (tp->unregfunc && static_key_enabled(&tp->key))
> > +		if (tp->unregfunc &&
> > +		    ((tp->dynamic && (atomic_read(&tp->key.enabled) > 0)) ||
> > +		     static_key_enabled(&tp->key)))
> > 			tp->unregfunc();
> > 
> > -		if (static_key_enabled(&tp->key))
> > +		if (tp->dynamic && (atomic_read(&tp->key.enabled) > 0))
> > +			atomic_dec(&tp->key.enabled);
> > +		else if (!tp->dynamic && static_key_enabled(&tp->key))
> > 			static_key_slow_dec(&tp->key);
> > 	}
> > 	rcu_assign_pointer(tp->funcs, tp_funcs);
> > @@ -258,7 +266,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> > }
> > 
> > /**
> > - * tracepoint_probe_register -  Connect a probe to a tracepoint
> > + * tracepoint_probe_register_prio -  Connect a probe to a tracepoint
> >  * @tp: tracepoint
> >  * @probe: probe handler
> >  * @data: tracepoint data
> 
> Hi Tom,
> 
> Thanks for updating your approach to dynamic tracepoints.
> 
> Since you're fixing up this comment above tracepoint_probe_register_prio,
> can you also remove the following line above tracepoint_probe_register
> while you are at it ?
> 

Sure, will do.

Thanks,

Tom