linux-kernel - Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier (x86) (v12)

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Message-ID: <20150317101009.78442f30@gandalf.local.home>
Date:	Tue, 17 Mar 2015 10:10:09 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC PATCH] sys_membarrier(): system/process-wide memory
 barrier (x86) (v12)

On Tue, 17 Mar 2015 04:44:11 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> On Tue, Mar 17, 2015 at 07:40:56AM +0100, Peter Zijlstra wrote:
> > On Mon, Mar 16, 2015 at 10:26:11PM -0400, Steven Rostedt wrote:
> > > As I recently found out that this_cpu_read/write() is not that nice on
> > > all architectures,
> > 
> > In fact, they only really work well on x86. Aargh64 seems to have a semi
> > usable version, but mostly its quite horrible indeed.
> 
> Yeah, if you are in a preempt-disabled region, __this_cpu_read() and
> __this_cpu_write() generate much better code on most platforms.
> 

I was just having this discussion with Christoph. I originally switched
to using this_cpu_ptr(), but I'll try __this_cpu* instead. I think
Christoph recommended that too.

-- Steve
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