From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [PATCH 0/3] x86_64, sfc: 128-bit memory-mapped I/O Date: Wed, 22 Aug 2012 02:43:03 +0100 Message-ID: <1345599783.2659.82.camel@bwh-desktop.uk.solarflarecom.com> References: <1345598275.2659.71.camel@bwh-desktop.uk.solarflarecom.com> <50343810.2000809@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Ingo Molnar , , , To: "H. Peter Anvin" Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:45279 "EHLO ocex02.SolarFlarecom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753215Ab2HVBnH (ORCPT ); Tue, 21 Aug 2012 21:43:07 -0400 In-Reply-To: <50343810.2000809@zytor.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2012-08-21 at 18:38 -0700, H. Peter Anvin wrote: > On 08/21/2012 06:17 PM, Ben Hutchings wrote: > > Current Solarflare network controllers have 128-bit memory-mapped > > registers which are normally accessed through a series of I/O > > operations. However, it is also possible to access them with a single > > MOVAPS instruction on x86_64, and this is measurably faster as it > > requires only one PCIe transaction. > > Also, have you considered doing this with write combining instead? We tried it, and it goes horribly wrong. On some systems, the writes are not combined, but they are reordered in a way the hardware doesn't support. See the comment at the top of drivers/net/ethernet/sfc/io.h. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.