Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933110AbaDILtQ (ORCPT ); Wed, 9 Apr 2014 07:49:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:39736 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932482AbaDILtP (ORCPT ); Wed, 9 Apr 2014 07:49:15 -0400 Date: Wed, 9 Apr 2014 13:48:57 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: David Ahern , Andi Kleen , Stephane Eranian , "Yan, Zheng" , LKML , Ingo Molnar , Arnaldo Carvalho de Melo Subject: Re: [PATCH v3 00/14] perf, x86: Haswell LBR call stack support Message-ID: <20140409114857.GT11096@twins.programming.kicks-ass.net> References: <1392703661-15104-1-git-send-email-zheng.z.yan@intel.com> <530D53EF.9090706@amacapital.net> <20140226185513.GL22728@two.firstfloor.org> <530E3E47.8010205@gmail.com> <530E4B42.5090401@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 26, 2014 at 12:26:43PM -0800, Andy Lutomirski wrote: > Speed. FPO saves one register (a big deal on x86_32; not so important > on x86_64) but also saves a few cycles on function entry and exit, > which is a bigger deal for small functions. So I though that LTO was supposed to get rid of a lot of the small function and inline them. I've also heard that in practise this is very 'hard', and thus we're still stuck with a gazillion small functions (mostly C++ people suffer from this). Can anybody give a concise explanation on why LTO doesn't rid us of these small functions or point to a web resource that describes the problem? -- 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/