linux-kernel - Re: x86 memory barrier: why does Linux prefer MFENCE to Locked ADD?

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Message-ID: <20160603133920.GA3913@twins.programming.kicks-ass.net>
Date:	Fri, 3 Jun 2016 15:39:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	"linux-x86_64@...r.kernel.org" <linux-x86_64@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	David Howells <dhowells@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: x86 memory barrier: why does Linux prefer MFENCE to Locked ADD?

On Thu, Mar 03, 2016 at 11:05:43AM -0800, H. Peter Anvin wrote:
> >> latest version here:
> >> 
> >>   lkml.kernel.org/r/1453921746-16178-1-git-send-email-mst@...hat.comZ
> >
> >It's ready as far as I am concerned.
> >Basically we are just waiting for ack from hpa.
> 
> And I'm still discussing this with the hardware people.  It seems we
> can do this for *most* things, but not all; the question is where
> exactly we need to do something different.

Anything on this?