From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764966AbYD0XRP (ORCPT ); Sun, 27 Apr 2008 19:17:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763933AbYD0XQx (ORCPT ); Sun, 27 Apr 2008 19:16:53 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:35801 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765310AbYD0XQw (ORCPT ); Sun, 27 Apr 2008 19:16:52 -0400 Date: Sun, 27 Apr 2008 16:11:05 -0700 From: Arjan van de Ven To: James Bottomley Cc: Ingo Molnar , Thomas Gleixner , linux-kernel Subject: Re: Breakage caused by unreviewed patch in x86 tree Message-ID: <20080427161105.0b452fe4@laptopd505.fenrus.org> In-Reply-To: <1209337439.3801.84.camel@localhost.localdomain> References: <1209329485.3801.46.camel@localhost.localdomain> <20080427155803.73f0efcf@laptopd505.fenrus.org> <1209337439.3801.84.camel@localhost.localdomain> Organization: Intel X-Mailer: Claws Mail 3.2.0 (GTK+ 2.12.5; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 27 Apr 2008 19:03:59 -0400 James Bottomley wrote: > On Sun, 2008-04-27 at 15:58 -0700, Arjan van de Ven wrote: > > On Sun, 27 Apr 2008 16:51:25 -0400 > > James Bottomley wrote: > > When you're mapping device memory, uncached is the safe default. > > Well, for certain device mailboxes, uncached does mean less > performant. The voyager breakage was exceptional ... I expect other > problems just to result in a loss of performance that caching gave by > improving the bursting. If we're lucky, the PCI bridge cache might > hide a lot of this. on a PC, NONE of the ioremap()s of PCI stuff were cached before, with the exception of prefetchable ranges, that some bioses set up a write-combining MTRR for. (and write-combining is effectively "uncached but with write buffering") If you look at at what kind of devices have prefetchable ranges, you get two answers: 1) video cards 2) some IB adapters So your argument that this might change PCI stuff is just false. Your argument that this "99.9%->100% uncached" should have been announced/discussed in public, sure. But to make this big a deal out of it? -- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org