From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e33.co.us.ibm.com ([32.97.110.151]:32890 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965808AbXDBUNX (ORCPT ); Mon, 2 Apr 2007 16:13:23 -0400 Subject: Re: [PATCH 1/4] x86_64: Switch to SPARSE_VIRTUAL From: Dave Hansen In-Reply-To: References: <20070401071024.23757.4113.sendpatchset@schroedinger.engr.sgi.com> <20070401071029.23757.78021.sendpatchset@schroedinger.engr.sgi.com> <200704011246.52238.ak@suse.de> Content-Type: text/plain Date: Mon, 02 Apr 2007 13:13:17 -0700 Message-Id: <1175544797.22373.62.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org To: Christoph Lameter Cc: Andi Kleen , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Martin Bligh , linux-mm@kvack.org, KAMEZAWA Hiroyuki List-ID: On Mon, 2007-04-02 at 08:37 -0700, Christoph Lameter wrote: > You want a benchmark to prove that the removal of memory references and > code improves performance? Yes, please. ;) I completely agree, it looks like it should be faster. The code certainly has potential benefits. But, to add this neato, apparently more performant feature, we unfortunately have to add code. Adding the code has a cost: code maintenance. This isn't a runtime cost, but it is a real, honest to goodness tradeoff. So, let's get some kind of concrete idea what the tradeoffs are. Is it, 400 lines of code gets us a 10% performance boost across the board, or that 400,000 lines gets us 0.1% on one specialized benchmark? BTW, I like the patches. Very nice and clean. -- Dave