linux-kernel - Re: [PATCH] rcu: use try_cmpxchg in check_cpu

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Message-ID: <CAEXW_YTRG+7oTGgmqSKpC6Wzft6vsjOzEDkN=eLpcEWeAxYwdg@mail.gmail.com>
Date:   Tue, 28 Feb 2023 19:45:30 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Uros Bizjak <ubizjak@...il.com>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] rcu: use try_cmpxchg in check_cpu_stall

Hey Steve,

On Tue, Feb 28, 2023 at 7:08 PM Steven Rostedt <rostedt@...dmis.org> wrote:
[...]
> >
> > >
> > > But in your case, we don't need to update js, in which case the
> > > try_cmpxchg() does.
> >
> > Right, it has lesser value here but I'm curious why you feel it also
> > doesn't belong in that ring buffer loop you shared (or did you mean,
> > it does belong there but not in other ftrace code modified by Uros?).
>
> The ring buffer patch had more than one change, where half the updates were
> fine, and half were not.

Thanks for all the clarifications. Good to know such loop design
patterns can benefit from it!


 - Joel