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

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Message-ID: <20230301154641.695778bf@gandalf.local.home>
Date:   Wed, 1 Mar 2023 15:46:41 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, 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

On Wed, 1 Mar 2023 12:36:45 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> Some years down the road, should cmpxchg_success() be on the tip of
> the tongue of every kernel hacker, perhaps.  Or perhaps not.

A bit of a catch-22 I would say. It will only become something everyone
knows if it exists.

> 
> In the meantime, we have yet another abysmally documented atomic

Is it?

> operation that is not well known throughout the community.  And then the
> people coming across this curse everyone who had anything to do with it,
> as they search the source code, dig through assembly output, and so on
> trying to work out exactly what this thing does.
> 
> Sorry, but no way.
> 
> Again, unless there is some sort of forward-progress argument or
> similar convincing argument.

Speaking of forward progress...

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/atomic_t.txt#n316

Anyway, I'm guessing this will not become part of rcu any time soon. But
for the ring buffer, I would happily take it.

-- Steve