Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936034AbXJPVZj (ORCPT ); Tue, 16 Oct 2007 17:25:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933703AbXJPVZ0 (ORCPT ); Tue, 16 Oct 2007 17:25:26 -0400 Received: from artax.karlin.mff.cuni.cz ([195.113.31.125]:56152 "EHLO artax.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933688AbXJPVZY (ORCPT ); Tue, 16 Oct 2007 17:25:24 -0400 Date: Tue, 16 Oct 2007 23:25:23 +0200 (CEST) From: Mikulas Patocka To: "H. Peter Anvin" cc: Arjan van de Ven , Nick Piggin , Linux Kernel Mailing List Subject: Re: LFENCE instruction In-Reply-To: <4714DBD7.7080706@zytor.com> Message-ID: References: <20071015143732.01d99af8@laptopd505.fenrus.org> <471401AF.4090802@zytor.com> <4714DBD7.7080706@zytor.com> X-Personality-Disorder: Schizoid MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1328 Lines: 34 On Tue, 16 Oct 2007, H. Peter Anvin wrote: > Mikulas Patocka wrote: > > > > PREFETCH* doesn't change program semantics. The processor is allowed to > > ignore prefetch instruction if it doesn't have resources needed for > > prefetch. It not ordered wrt. fences. > > > > PREFETCHNTA was implemented as prefetch into L1 cache and omitting L2 cache > > on Pentium 3 and M --- and it is implemented as prefetch into L2 cache on > > other --- do it doesn't really use any special buffers. > > > > It's semantics allows it to, though. It's not clear to me whether it is > actually necessary on existing chips. > > It does, I believe, way-restricted prefetch on existing silicon. It is allowed to use special buffers for prefetch, but --- because prefetch doesn't change program semantics, these special buffers must be kept consistent just like caches --- they must be snooped for bus transactions and they must be checked each time something writes to cache. So I doubt anyone will ever implement it this way --- it's too much silicon for too little effect. Mikulas > -hpa - 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/