Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755484AbXI1QPv (ORCPT ); Fri, 28 Sep 2007 12:15:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752759AbXI1QPn (ORCPT ); Fri, 28 Sep 2007 12:15:43 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:50683 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751862AbXI1QPm (ORCPT ); Fri, 28 Sep 2007 12:15:42 -0400 Date: Fri, 28 Sep 2007 09:15:06 -0700 (PDT) From: Linus Torvalds To: Alan Cox cc: Nick Piggin , Linux Kernel Mailing List , Andi Kleen Subject: Re: [patch] x86: improved memory barrier implementation In-Reply-To: <20070928170719.2f617a7a@the-village.bc.nu> Message-ID: References: <20070928154832.GB12538@wotan.suse.de> <20070928170719.2f617a7a@the-village.bc.nu> 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: 980 Lines: 31 On Fri, 28 Sep 2007, Alan Cox wrote: > > However > - You've not shown the patch has any performance gain It would be nice to see this. > - You've probably broken Pentium Pro Probably not a big deal, but yeah, we should have that broken-ppro option. > - and for modern processors its still not remotely clear your patch is > correct because of NT stores. This one I disagree with. The *old* code doesn't honor NT stores *either*. The fact is, if you use NT stores and then depend on ordering, it has nothing what-so-ever to do with spinlocks or smp_[rw]mb. You need to use the DMA barriers (ie the non-smp ones). The non-temporal stores should be basically considered to be "IO", not any normal memory operation. Linus - 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/