Date:   Wed, 1 Mar 2023 15:18:26 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Uros Bizjak <ubizjak@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] rcu: use try_cmpxchg in check_cpu_stall
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On Wed, 1 Mar 2023 12:08:20 -0800
"Paul E. McKenney" <paulmck@kernel.org> wrote:

> > Attached patch implements this suggestion.  
> 
> Please help me out here.
> 
> Why on earth are we even discussing making this change to code that
> normally never executes?  Performance is not a consideration here.
> 
> What am I missing here?  Is there some sort of forward-progress
> issue that this change addresses?

Well, we sorta hijacked this thread. It turned into a more general
discussion, as there is code that this change will be useful for
(ring_buffer.c), but we just happen to be having the discussion here.

Where it will at most remove some text and give you back a few extra bytes
of memory ;-)

But if we do use cmpxchg_success() IMHO, it does improve readability.

> -	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
> +	    cmpxchg_success(&rcu_state.jiffies_stall, js, jn)) {

-- Steve