linux-kernel - Re: [GIT PULL] ring-buffer: Replace this_cpu_*() with __this_cpu

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Message-ID: <alpine.DEB.2.11.1503241343470.32546@gentwo.org>
Date:	Tue, 24 Mar 2015 13:47:06 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	stable <stable@...r.kernel.org>,
	Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>
Subject: Re: [GIT PULL] ring-buffer: Replace this_cpu_*() with
 __this_cpu_*()

On Mon, 23 Mar 2015, Steven Rostedt wrote:

> Any comment on this?

Yes we could do this but I am traveling a bit right now. Sorry not that
responsive.

It will not be strictly correct since a fetch or write could occur from a
different cpu and thereby kick out a cacheline. But that is minor I think.

The main issue is that this makes this_cpu_read/write different from other
this_cpu operations which guarantee that these are "per cpu atomic" in the
sense that they are either completely executed or not. But that is mostly
important for this_cpu_ ops that are RMV operations like this_cpu_inc().

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