From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759630AbZKFT0O (ORCPT ); Fri, 6 Nov 2009 14:26:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759271AbZKFT0O (ORCPT ); Fri, 6 Nov 2009 14:26:14 -0500 Received: from terminus.zytor.com ([198.137.202.10]:39803 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755692AbZKFT0N (ORCPT ); Fri, 6 Nov 2009 14:26:13 -0500 Message-ID: <4AF4784C.5090800@zytor.com> Date: Fri, 06 Nov 2009 11:26:04 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20091014 Fedora/3.0-2.8.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: ling.ma@intel.com CC: mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by fast string. References: <1257500482-16182-1-git-send-email-ling.ma@intel.com> <4AF457E0.4040107@zytor.com> In-Reply-To: <4AF457E0.4040107@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/06/2009 09:07 AM, H. Peter Anvin wrote: > > Where did the 1024 byte threshold come from? It seems a bit high to me, > and is at the very best a CPU-specific tuning factor. > > Andi is of course correct that older CPUs might suffer (sadly enough), > which is why we'd at the very least need some idea of what the > performance impact on those older CPUs would look like -- at that point > we can make a decision to just unconditionally do the rep movs or > consider some system where we point at different implementations for > different processors -- memcpy is probably one of the very few > operations for which something like that would make sense. > To be expicit: Ling, would you be willing to run some benchmarks across processors to see how this performs on non-Nehalem CPUs? -hpa