linux-kernel - Re: [PATCH] tracing: Remove pointless memory barriers

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Message-ID: <20250721204932.306da76c@gandalf.local.home>
Date: Mon, 21 Jul 2025 20:49:32 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Nam Cao <namcao@...utronix.de>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org, Gabriele Monaco <gmonaco@...hat.com>,
 john.ogness@...utronix.de
Subject: Re: [PATCH] tracing: Remove pointless memory barriers

On Thu, 26 Jun 2025 18:04:59 +0200
Nam Cao <namcao@...utronix.de> wrote:

> > The above three interact with each other. Without the barriers, the
> > tr->buffer_disabled = 0, can be set on one CPU, and the other CPU can think
> > the buffer is still enabled and do work that will end up doing nothing. Or
> > it can be set to 1, and the other CPU still sees it disabled and will not
> > do work when it can.  
> 
> (I'm not that experienced with memory barrier, so I may be writing nonsense
> here)

So I did some git archeology and realized that the buffer_disabled is just
a cache to make irqsoff tracing faster. The commit even said it's not going
to be accurate.

OK, I'll just take this patch.

Thanks,

-- Steve