linux-kernel - Re: [PATCH v2 27/27] context_tracking, rcu: Rename rcu_dyntick trace event into rcu

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Date: Tue, 14 May 2024 14:09:25 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH v2 27/27] context_tracking, rcu: Rename rcu_dyntick trace
 event into rcu_watching

Le Mon, May 13, 2024 at 08:40:42PM +0200, Valentin Schneider a écrit :
> On 08/05/24 15:59, Frederic Weisbecker wrote:
> > Le Tue, Apr 30, 2024 at 11:17:31AM +0200, Valentin Schneider a écrit :
> >> @@ -228,7 +228,7 @@ void noinstr ct_nmi_exit(void)
> >>      }
> >>
> >>      /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
> >> -	trace_rcu_dyntick(TPS("Startirq"), ct_nmi_nesting(), 0, ct_rcu_watching());
> >> +	trace_rcu_watching(TPS("Endirq"), ct_nmi_nesting(), 0, ct_rcu_watching());
> >
> > Ah the initial string was wrong and you're fixing it, right?
> >
> > Should be a seperate patch?
> >
> 
> No, I'm just creating confusion for everyone involved (including myself) :(
> Dynticks start when RCU stops watching, so the naming logic gets flipped on
> its head.
> 
> If I take the original comment from
> bd2b879a1ca5 ("rcu: Add tracing to irq/NMI dyntick-idle transitions")
> """
> as argument: "Start" for entering dyntick-idle mode, "Startirq" for
> entering it from irq/NMI
> """

Oh my!

> 
> So here "Startirq" means "start dyntick mode from IRQ". With the name
> change, it should be "Endirq", since RCU stops watching, from IRQ...
> 
> I know, a lot of confusion for 0 functional change :(

Ok your change looks good then.

Thanks.