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

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Message-ID: <20160803231955.GA9304@khazad-dum.debian.net>
Date:	Wed, 3 Aug 2016 20:19:55 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Wed, 03 Aug 2016, Michael S. Tsirkin wrote:
> Are any of these used in kernel though?

These specific errata were not the point of my post, rather, it was the
fact that errata related to *FENCE and LOCKed instructions exists.

I didn't verify whether something attempts to use non-temporal loads or
stores from WC memory in the kernel.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh