From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935162AbYDQKJO (ORCPT ); Thu, 17 Apr 2008 06:09:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934510AbYDQKGh (ORCPT ); Thu, 17 Apr 2008 06:06:37 -0400 Received: from out1.smtp.messagingengine.com ([66.111.4.25]:37665 "EHLO out1.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1764845AbYDQKGe (ORCPT ); Thu, 17 Apr 2008 06:06:34 -0400 Message-Id: <1208426793.10305.1248377703@webmail.messagingengine.com> X-Sasl-Enc: wq4t9ndhwgpKrEtA2h+yA3/B2cS2QumDAKhFWl7vP99o 1208426793 From: "Alexander van Heukelum" To: "Andi Kleen" , "Ingo Molnar" Cc: linux-kernel@vger.kernel.org Content-Disposition: inline Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="ISO-8859-1" MIME-Version: 1.0 X-Mailer: MessagingEngine.com Webmail Interface References: <20080416202338.GA6007@elte.hu> <878wzdikwk.fsf@basil.nowhere.org> Subject: Re: [v2.6.26] what's brewing in x86.git for v2.6.26 In-Reply-To: <878wzdikwk.fsf@basil.nowhere.org> Date: Thu, 17 Apr 2008 12:06:33 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 16 Apr 2008 22:50:51 +0200, "Andi Kleen" said: > Ingo Molnar writes: > > > - generalized bitops - they are faster and smaller. > > Faster in a 100% bogus benchmark with the most unrealistic input data > set one can imagine with some effort. They might be faster or they > might be slower, nobody really knows currently. Hello Andi, Ingo, The input for the first 'benchmark' was indeed completely unrealistic. They did show a very convincing speedup, though. This program was really written to verify the implementation and was later converted to a benchmark. Many benchmarks are unrealistic. I also wrote a benchmark for find_first_bit and find_next_bit: http://heukelum.fastmail.fm/find_first_bit My conclusion would be: the speed of the generic bitmap implementation is either better than or at least comparable to the current private implementations in i386/x86_64. The generic version is out-of-line, while the private implementation of i386 was inlined: this causes a regression for very small bitmaps. However, if the bitmap size is a constant and fits a long integer, the updated generic code should inline an optimized version, like x86_64 currently does it. I think the change is a good one. Greetings, Alexander -- Alexander van Heukelum heukelum@fastmail.fm -- http://www.fastmail.fm - The professional email service