From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: [PATCH 05/10] xen: use SMP barrier in common code dealing with shared memory protocols Date: Thu, 4 Jul 2013 12:26:29 +0100 Message-ID: <20130704112629.GG40611@ocelot.phlegethon.org> References: <1372435809.8976.169.camel@zakaz.uk.xensource.com> <1372435856-14040-5-git-send-email-ian.campbell@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1372435856-14040-5-git-send-email-ian.campbell@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: julien.grall@citrix.com, stefano.stabellini@eu.citrix.com, keir@xen.org, jbeuich@suse.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org At 17:10 +0100 on 28 Jun (1372439451), Ian Campbell wrote: > Xen currently makes no strong distinction between the SMP barriers (smp_mb > etc) and the regular barrier (mb etc). In Linux, where we inherited these > names from having imported Linux code which uses them, the SMP barriers are > intended to be sufficient for implementing shared-memory protocols between > processors in an SMP system while the standard barriers are useful for MMIO > etc. > > On x86 with the stronger ordering model there is not much practical difference > here but ARM has weaker barriers available which are suitable for use as SMP > barriers. > > Therefore ensure that common code uses the SMP barriers when that is all which > is required. > > On both ARM and x86 both types of barrier are currently identical so there is > no actual change. A future patch will change smp_mb to a weaker barrier on > ARM. > > Signed-off-by: Ian Campbell Reviewed-by: Tim Deegan