Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752838AbaDXTfH (ORCPT ); Thu, 24 Apr 2014 15:35:07 -0400 Received: from top.free-electrons.com ([176.31.233.9]:40596 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752758AbaDXTfB (ORCPT ); Thu, 24 Apr 2014 15:35:01 -0400 Message-ID: <53596762.5070806@free-electrons.com> Date: Thu, 24 Apr 2014 21:34:58 +0200 From: Michael Opdenacker User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Josh Triplett CC: akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, fweisbec@gmail.com, eparis@redhat.com, paul.gortmaker@windriver.com, vapier@gentoo.org, kyungsik.lee@lge.com, jslaby@suse.cz, dwight.engen@oracle.com, pefoley2@pefoley.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/1] init/Kconfig: improve CC_OPTIMIZE_FOR_SIZE documentation References: <1398341254-4626-1-git-send-email-michael.opdenacker@free-electrons.com> <20140424145535.GA2969@jtriplet-mobl1> In-Reply-To: <20140424145535.GA2969@jtriplet-mobl1> X-Enigmail-Version: 1.5.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Josh, Thank you for your review! On 04/24/2014 04:55 PM, Josh Triplett wrote: > On Thu, Apr 24, 2014 at 02:07:33PM +0200, Michael Opdenacker wrote: >> This patch proposes to warn users about the negative performance >> impact of CC_OPTIMIZE_FOR_SIZE (compiling with -Os instead of -O2). >> For the moment, we are just advising users not to select this option, >> but extra details would be useful. >> >> I made some experiments with this option. All of them yielded >> degraded overall boot time. The kernel is smaller and hence is copied >> and started earlier, but the benefits are quickly offset by the >> slower kernel code. Even the total boot time is usually worse >> than with a regular kernel. >> >> Here are my latest results, on Atmel SAMA5D3 Xplained (ARM), >> Linux 3.10, gzip compressed kernel: >> >> Timestamp O2 Os Diff >> Starting kernel 4.307 s 5.593 s -94 ms >> Starting init 4.213 s 5.549 s -44 ms >> Login prompt 21.085 s 22.900 s +1.815 s > Did you get the times in the upper two rows transposed row/column? Based > on the diffs, I'd guess 4.213s goes in Os "Starting kernel", and 5.593s > goes in O2 "Starting init". Oops, yes I did. I shouldn't have tried to copy from a PDF file I produced ;) Thanks! Michael. -- Michael Opdenacker, CEO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- 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/