linux-kernel - Re: [PATCH v3 13/22] tracing: Remove regular RCU context for

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Message-ID: <20200219174025.GJ2935@paulmck-ThinkPad-P72>
Date:   Wed, 19 Feb 2020 09:40:25 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v3 13/22] tracing: Remove regular RCU context for
 _rcuidle tracepoints (again)

On Wed, Feb 19, 2020 at 12:21:16PM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2020 18:05:07 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, Feb 19, 2020 at 05:47:36PM +0100, Peter Zijlstra wrote:
> > > On Wed, Feb 19, 2020 at 08:43:56AM -0800, Paul E. McKenney wrote:  
> > > > On Wed, Feb 19, 2020 at 03:47:37PM +0100, Peter Zijlstra wrote:  
> > > > > Effectively revert commit 865e63b04e9b2 ("tracing: Add back in
> > > > > rcu_irq_enter/exit_irqson() for rcuidle tracepoints") now that we've
> > > > > taught perf how to deal with not having an RCU context provided.
> > > > > 
> > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > > > ---
> > > > >  include/linux/tracepoint.h |    8 ++------
> > > > >  1 file changed, 2 insertions(+), 6 deletions(-)
> > > > > 
> > > > > --- a/include/linux/tracepoint.h
> > > > > +++ b/include/linux/tracepoint.h
> > > > > @@ -179,10 +179,8 @@ static inline struct tracepoint *tracepo  
> > > > 
> > > > Shouldn't we also get rid of this line above?
> > > > 
> > > > 		int __maybe_unused __idx = 0;				\
> > > >   
> > > 
> > > Probably makes a lot of sense, lemme fix that!  
> > 
> > Oh wait, no! SRCU is the one that remains !
> 
> Correct, and if rcuidle is not set, and this is a macro, the SRCU
> portion is compiled out.

Sigh!  Apologies for the noise!

If we are using SRCU, we don't care whether or not RCU is watching.  OK,
maybe finally catching up -- the whole point was use of RCU in other
tracing code, wasn't it?

						Thanx, Paul