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

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Date: Mon, 13 May 2024 20:40:42 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
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

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
"""

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 :(