From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933145Ab2AFJt2 (ORCPT ); Fri, 6 Jan 2012 04:49:28 -0500 Received: from one.firstfloor.org ([213.235.205.2]:46857 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933000Ab2AFJt0 (ORCPT ); Fri, 6 Jan 2012 04:49:26 -0500 Date: Fri, 6 Jan 2012 10:49:22 +0100 From: Andi Kleen To: "H. Peter Anvin" Cc: Andi Kleen , Jan Beulich , mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org Subject: Re: x86-64: memset()/memcpy() not fully standards compliant Message-ID: <20120106094922.GU11715@one.firstfloor.org> References: <4F05BBFE020000780006A983@nat28.tlf.novell.com> <20120105182846.GQ11715@one.firstfloor.org> <4F0630CC.7050001@zytor.com> <20120106014748.GS11715@one.firstfloor.org> <4F06566B.8080708@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F06566B.8080708@zytor.com> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 05, 2012 at 06:03:23PM -0800, H. Peter Anvin wrote: > On 01/05/2012 05:47 PM, Andi Kleen wrote: > >> > >> Is that still true, and do we even use string instructions still on > >> those old CPUs? Jan's fixes don't introduce any additional delays in > >> the non-string-instruction paths. > > > > Yes various of the CPUs with bugs used string instructions. > > > > Which CPUs are you talking about here? This was various iterations of K8 and PSC. Early Meroms may also have had issues (not 100% sure). > > > > > Both string and non string instructions are used on modern CPUs, > > so making any of that slower is not a good idea. > > > > Obviously not, but I'm perfectly fine turning REP_GOOD off on old broken > CPUs. That would be even worse. You would slow a critical fast path operation down for something that never happens?!? There were big differences between strings and the unrolled loop for several. IMHO it's a war games situation: "the only way to win is not to play" -Andi