Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756503Ab1E0QxK (ORCPT ); Fri, 27 May 2011 12:53:10 -0400 Received: from mga02.intel.com ([134.134.136.20]:64078 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754210Ab1E0QxG (ORCPT ); Fri, 27 May 2011 12:53:06 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,281,1304319600"; d="scan'208";a="5930386" Message-ID: <4DDFD6F2.1040304@linux.intel.com> Date: Fri, 27 May 2011 09:53:06 -0700 From: Andi Kleen User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.15) Gecko/20110303 Thunderbird/3.1.9 MIME-Version: 1.0 To: Will Deacon CC: Nicolas Pitre , Catalin Marinas , =?UTF-8?B?TcOlbnMgUnVsbGfDpXJk?= , linux-arm-kernel@lists.infradead.org, lkml , Andrew Morton , sam@ravnborg.org Subject: Re: [PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP References: <20110523111648.10474.78396.stgit@e102109-lin.cambridge.arm.com> <20110523132124.GI17672@n2100.arm.linux.org.uk> <1306229953.19557.14.camel@e102109-lin.cambridge.arm.com> <20110524171331.GA2941@arm.com> <20110525111405.GA12010@e102109-lin.cambridge.arm.com> <20110525124348.GA2340@arm.com> <1306429854.26735.9.camel@e102144-lin.cambridge.arm.com> <4DDEC1C0.20807@linux.intel.com> <1306490709.26257.4.camel@e102144-lin.cambridge.arm.com> In-Reply-To: <1306490709.26257.4.camel@e102144-lin.cambridge.arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1050 Lines: 28 > Do you have any concrete examples of -fconserve-stack giving an overall > win that isn't in the noise? The fact that the GCC documentation > explicitly states that enabling the option can lead to `making the > program slower' does make me question why we're enabling it in the first > place. Because the kernel has a limited stack. We had a few cases in the past where inlining blew it, especially in large ioctl switch() functions which inlined lots of others. On modern gccs it's better because it is smarter about sharing stack slots in large functions. This was also worked around with manual noinlines. But it's still far safer to tell gcc to conserve stack. I consider the ARM gcc behaviour just a bug. The thing was really only intended for the inliner (I asked for it originally) -Andi -- 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/