linux-kernel - Re: [PATCH v2] ring-buffer: Replace this_cpu_*() with __this_cpu

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Message-ID: <20150319124023.4c1b1094@gandalf.local.home>
Date:	Thu, 19 Mar 2015 12:40:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v2] ring-buffer: Replace this_cpu_*() with
 __this_cpu_*()

On Thu, 19 Mar 2015 11:33:30 -0500 (CDT)
Christoph Lameter <cl@...ux.com> wrote:

> If you are redoing it then please get the comments a bit cleared up. The

What comments should I clear up? This version did not have a comment.
It just switched this_cpu_* to __this_cpu_*, and also updated a
variable algorithm.

-- Steve


> heaviness of the fallback version of this_cpu_read/write can usually
> easily be remedied by arch specific definitions. The per cpu
> offset is somewhere in a register and one needs to define a macro that
> creates an instruction that does a fetch from that register plus
> the current offset into the area that is needed. This is similarly easy
> for the write path. But then its often easier to just use the __this_cpu
> instructions since preemption is often off in these code paths.
> 
> I have had code for IA64 in the past that does this.

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