Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757818AbaDXOzv (ORCPT ); Thu, 24 Apr 2014 10:55:51 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:50484 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753344AbaDXOzt (ORCPT ); Thu, 24 Apr 2014 10:55:49 -0400 X-Originating-IP: 50.43.32.211 Date: Thu, 24 Apr 2014 07:55:35 -0700 From: Josh Triplett To: Michael Opdenacker 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 Message-ID: <20140424145535.GA2969@jtriplet-mobl1> References: <1398341254-4626-1-git-send-email-michael.opdenacker@free-electrons.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1398341254-4626-1-git-send-email-michael.opdenacker@free-electrons.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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". - Josh Triplett -- 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/