From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761301AbZENRXw (ORCPT ); Thu, 14 May 2009 13:23:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755278AbZENRXd (ORCPT ); Thu, 14 May 2009 13:23:33 -0400 Received: from one.firstfloor.org ([213.235.205.2]:45154 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757289AbZENRXc (ORCPT ); Thu, 14 May 2009 13:23:32 -0400 Date: Thu, 14 May 2009 19:29:01 +0200 From: Andi Kleen To: Ulrich Drepper Cc: Andi Kleen , Harvey Harrison , Tobias Doerffel , LKML Subject: Re: Specific support for Intel Atom architecture Message-ID: <20090514172901.GH10933@one.firstfloor.org> References: <200904301408.09370.tobias.doerffel@gmail.com> <877i0xib7d.fsf@basil.nowhere.org> <20090512150408.GH19296@one.firstfloor.org> <1242277453.23058.35.camel@brick> <20090514140138.GB10933@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 14, 2009 at 09:19:38AM -0700, Ulrich Drepper wrote: > On Thu, May 14, 2009 at 7:01 AM, Andi Kleen wrote: > > How would you test that? > > Compare runtimes with mov+bswap for some simple code which uses the > value after the conversion (e.g., just add to something). > > Or in your case: get the Atom designers to comment. Don't really need Atom designers; you can prove or disprove my theory (that they generate the same uops sequence) by checking the uops performance counter for a micro benchmark. However even if that was not the case I have some doubts the kernel is doing enough endian conversions that it really matters. For example the network stack is doing maybe 4-5 endian conversions (very conservative estimate) per packet and processing a packet takes tens of thousands of cycles. But at best you could save 1-2 cycles this way, so even if you save a few cycles this way it will be very likely in the noise. -Andi -- ak@linux.intel.com -- Speaking for myself only.