linux-kernel - Re: [PATCH 0/3] tracing: introduce TRACE_EVENT

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Date:   Tue, 26 Mar 2019 10:24:35 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...hat.com, Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        josh@...htriplett.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        shaoyafang@...iglobal.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] tracing: introduce TRACE_EVENT_NONE and use it

On Tue, Mar 26, 2019 at 10:17 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 26 Mar 2019 09:40:04 +0800
> Yafang Shao <laoar.shao@...il.com> wrote:
>
> > In this patchset, I introduce a new macro TRACE_EVENT_NONE(), which will
> > define a tracepoint as a do-nothing inline function.
> >       #define TRACE_EVENT_NONE(name, proto)                   \
> >               static inline void trace_##name(proto)          \
> >               { }                                             \
> >               static inline bool trace_##name##_enabled(void) \
> >               {                                               \
> >                       return false;                           \
> >               }
> >
>
> BTW, I prefer a name of TRACE_EVENT_DISABLED()
>
> Which shows that it is disabled, or TRACE_EVENT_UNDEF(), or
> TRACE_EVENT_NOP(). Something that states it is turned off. When I first
> saw NONE() I thought it was another attempt to introduce zero parameter
> trace events.
>

I prefer TRACE_EVENT_NOP.
I will change it.

Thanks
Yafang

>
> > Let's take some example for why this macro is needed.
> >
> > - sched
> > The tracepoints trace_sched_stat_{iowait, blocked, wait, sleep} should
> > be not exposed to user if CONFIG_SCHEDSTATS is not set.
> > We can place #ifdef in the kernel/sched/fair.c to fix it, but we
> > don't want to sprinkle #ifdef.
>
> But you still sprinkle #ifdef in the header, but the part I don't like
> is the need to duplicate the prototypes and the like.
>
>
> > So with TRACE_EVENT_NONE(), we can fix it in
> > include/trace/events/sched.h.
> >
> > - rcu
> > When CONFIG_RCU_TRACE is not set, some rcu tracepoints are define as
> > do-nothing macro without validating arguments, that is not proper.
> > We should validate the arguments.
> >
> > Yafang Shao (3):
> >   tracing: introduce TRACE_EVENT_NONE()
> >   sched/fair: do not expose some tracepoints to user if
> >     CONFIG_SCHEDSTATS is not set
> >   rcu: validate arguments for rcu tracepoints
> >
>
> See my reply in the next patch.
>
> -- Steve