Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754227AbZLAQQR (ORCPT ); Tue, 1 Dec 2009 11:16:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753518AbZLAQQQ (ORCPT ); Tue, 1 Dec 2009 11:16:16 -0500 Received: from terminus.zytor.com ([198.137.202.10]:56467 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754053AbZLAQQO (ORCPT ); Tue, 1 Dec 2009 11:16:14 -0500 Message-ID: <4B154018.4060605@zytor.com> Date: Tue, 01 Dec 2009 08:11:04 -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: Arjan van de Ven CC: "Ma, Ling" , Ingo Molnar , Dave Jones , "tglx@linutronix.de" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH RFC] [X86] Compile Option Os versus O2 on latest x86 platform References: <1259222752-8161-1-git-send-email-ling.ma@intel.com> <20091126094930.GD32275@elte.hu> <8FED46E8A9CA574792FC7AACAC38FE7714FED213BE@PDSMSX501.ccr.corp.intel.com> <20091201021459.43d2142a@infradead.org> In-Reply-To: <20091201021459.43d2142a@infradead.org> 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 Content-Length: 1408 Lines: 36 On 12/01/2009 02:14 AM, Arjan van de Ven wrote: > On Tue, 1 Dec 2009 16:54:04 +0800 > "Ma, Ling" wrote: > >> Hi Ingo >> >> Thanks for your correction, so we use perf stat --repeat 3 to test >> volano, tbench, and kbuild, Because netperf has multiple items we may >> send out later. > > a key question is.. how much more memory do you have free due to -Os? > (because memory is cache is performance on a system level as well) > and how much less icache pressure is there? > >From the re-run, it sounds like the only test that actually shows a significant difference is volano. From reading the numbers, it looks like the improvements are almost exclusively in IPC i.e. better scheduling -- all the other metrics are substantially worse; including a 10% increase in cache misses. It would be interesting to see what functions are hot in volano. It might very well be that we could get a boost without significantly bloat the kernel as a whole by picking out a couple of hot object files and compiling those with -O2 or -O3. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/