Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754413Ab0BRU2D (ORCPT ); Thu, 18 Feb 2010 15:28:03 -0500 Received: from one.firstfloor.org ([213.235.205.2]:60913 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751425Ab0BRU17 (ORCPT ); Thu, 18 Feb 2010 15:27:59 -0500 Date: Thu, 18 Feb 2010 21:27:54 +0100 From: Andi Kleen To: "H. Peter Anvin" Cc: Andi Kleen , Jerome Glisse , suresh.b.siddha@intel.com, venkatesh.pallipadi@intel.com, thellstrom@vmware.com, airlied@linux.ie, currojerez@riseup.net, linux-kernel@vger.kernel.org Subject: Re: Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages Message-ID: <20100218202753.GI5964@basil.fritz.box> References: <20100218153032.GA4506@localhost.localdomain> <87aav65u9g.fsf@basil.nowhere.org> <4B7D7AF9.9060600@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B7D7AF9.9060600@zytor.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1182 Lines: 28 On Thu, Feb 18, 2010 at 09:38:01AM -0800, H. Peter Anvin wrote: > On 02/18/2010 09:27 AM, Andi Kleen wrote: > > Jerome Glisse writes: > >> > >> Can we modify the interface to support again changing from uc to wc > >> or wc to uc ? (i can try to do a patch for that). > > > > At least on Intel CPUs that support self-snoop (all modern > > ones) that should really be very cheap. > > > > The UC/WC transition should be particularly trivial; I don't see any > reason it should have to go through any other procedure on *any* CPU -- > selfsnoop shouldn't even figure into it, since neither UC nor WC > actually caches anything. For the WC->UC direction, all we should need > to do is to flush the write combiners; a simple wmb() will do that. I'm not sure that is sanctioned by the SDM rules; AFAIK they don't make any special exception for this case. -Andi -- ak@linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/