From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 2/3] x86_64: Define 128-bit memory-mapped I/O operations Date: Wed, 22 Aug 2012 08:54:00 -0700 Message-ID: <50350098.6030100@zytor.com> References: <1345598601.2659.76.camel@bwh-desktop.uk.solarflarecom.com> <503437D4.8090706@zytor.com> <1345601051.2659.93.camel@bwh-desktop.uk.solarflarecom.com> <20120821.193446.1534561579811962053.davem@davemloft.net> <503450E2.2040504@zytor.com> <1345642009.15245.0.camel@deadeye.wl.decadent.org.uk> <1345645499.15245.8.camel@deadeye.wl.decadent.org.uk> <20120822143054.GD9803@kvack.org> <1345647537.2709.0.camel@bwh-desktop.uk.solarflarecom.com> <5034F725.2090802@zytor.com> <1345650689.2709.32.camel@bwh-desktop.uk.solarflarecom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: David Laight , Benjamin LaHaise , Linus Torvalds , David Miller , tglx@linutronix.de, mingo@redhat.com, netdev@vger.kernel.org, linux-net-drivers@solarflare.com, x86@kernel.org To: Ben Hutchings Return-path: Received: from terminus.zytor.com ([198.137.202.10]:43568 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753851Ab2HVPyS (ORCPT ); Wed, 22 Aug 2012 11:54:18 -0400 In-Reply-To: <1345650689.2709.32.camel@bwh-desktop.uk.solarflarecom.com> Sender: netdev-owner@vger.kernel.org List-ID: On 08/22/2012 08:51 AM, Ben Hutchings wrote: >> >> FWIW can you even guarantee to do an atomic 64bit PCIe transfer >> on many systems (without resorting to a dma unit). > > On any architecture that implements readq and writeq these had better be > atomic. > Sorry, you fail. There are definitely systems in the field where readq() and writeq() are implemented, because the CPU supports them, where the fabric does not guarantee they are intact. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.