From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: MMIO and gcc re-ordering issue Date: Wed, 4 Jun 2008 12:47:14 +0100 Message-ID: <20080604124714.55dbce65@core> References: <1211852026.3286.36.camel@pasglop> <200806041205.45833.nickpiggin@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Linus Torvalds Cc: Nick Piggin , Trent Piepho , Russell King , Benjamin Herrenschmidt , David Miller , linux-arch@vger.kernel.org, scottwood@freescale.com, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org > Anyway, Intel certainly seems to document that WC memory is serialize= d by=20 > any access to UC memory. I don't believe that is actually true on Pentium Pro at least. > So what started out as a "we can do accesses to the frame buffer mo= re=20 > efficiently without anybody ever even having to know or care" has=20 > turned into a whole nightmare of people using it for other things, = and=20 > then you very much _do_ have to care! ] Notably graphics where 3Dfx lined the registers up specifically to make this work. We were also using it with I=C2=B2O where it gave a small performance gain. Alan From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:55954 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750764AbYFDMDC convert rfc822-to-8bit (ORCPT ); Wed, 4 Jun 2008 08:03:02 -0400 Date: Wed, 4 Jun 2008 12:47:14 +0100 From: Alan Cox Subject: Re: MMIO and gcc re-ordering issue Message-ID: <20080604124714.55dbce65@core> In-Reply-To: References: <1211852026.3286.36.camel@pasglop> <200806041205.45833.nickpiggin@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds Cc: Nick Piggin , Trent Piepho , Russell King , Benjamin Herrenschmidt , David Miller , linux-arch@vger.kernel.org, scottwood@freescale.com, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org Message-ID: <20080604114714.dcLQ0HoJQ2Zxnvl2IkVlH6aWrryP9KjkzvH13p13uRE@z> > Anyway, Intel certainly seems to document that WC memory is serialized by > any access to UC memory. I don't believe that is actually true on Pentium Pro at least. > So what started out as a "we can do accesses to the frame buffer more > efficiently without anybody ever even having to know or care" has > turned into a whole nightmare of people using it for other things, and > then you very much _do_ have to care! ] Notably graphics where 3Dfx lined the registers up specifically to make this work. We were also using it with I²O where it gave a small performance gain. Alan