From: Steven Rostedt <rostedt@goodmis.org>
To: David Laight <david.laight.linux@gmail.com>
Cc: Nam Cao <namcao@linutronix.de>,
Gabriele Monaco <gmonaco@redhat.com>,
John Ogness <john.ogness@linutronix.de>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tracing: Remove pointless memory barriers
Date: Fri, 11 Jul 2025 12:07:58 -0400 [thread overview]
Message-ID: <20250711120758.3f6904e9@batman.local.home> (raw)
In-Reply-To: <20250711092946.1bbd58ef@pumpkin>
On Fri, 11 Jul 2025 09:29:46 +0100
David Laight <david.laight.linux@gmail.com> wrote:
> > Doesn't atomic make sure the values are seen when they are changed?
>
> No.
> It normally just ensures the read/write aren't 'torn'.
> Atomics are used for read-modify-writes to ensure two cpu don't
> do read-read-modify-modify-write-write losing one of the changes.
> (They can need special instructions for read and write - but normally don't.)
> So here just the same as the volatile accesses READ_ONCE() and WRITE_ONCE().
At first I was about to say "But wait! I rely on this to work in other
parts of my code", but then realized I use atomic_inc_return() and
similar that actually do make the update atomic across CPUs.
-- Steve
next prev parent reply other threads:[~2025-07-11 16:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-26 15:19 [PATCH] tracing: Remove pointless memory barriers Nam Cao
2025-06-26 15:35 ` Steven Rostedt
2025-06-26 15:37 ` Steven Rostedt
2025-06-26 16:04 ` Nam Cao
2025-06-26 16:34 ` Steven Rostedt
2025-06-26 17:41 ` John Ogness
2025-07-03 8:05 ` Gabriele Monaco
2025-07-08 7:42 ` Nam Cao
2025-07-09 15:08 ` Steven Rostedt
2025-07-11 8:29 ` David Laight
2025-07-11 16:07 ` Steven Rostedt [this message]
2025-07-09 8:22 ` David Laight
2025-07-22 0:49 ` Steven Rostedt
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