Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753706AbaBZU1J (ORCPT ); Wed, 26 Feb 2014 15:27:09 -0500 Received: from mail-ve0-f177.google.com ([209.85.128.177]:51658 "EHLO mail-ve0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753539AbaBZU1H (ORCPT ); Wed, 26 Feb 2014 15:27:07 -0500 MIME-Version: 1.0 In-Reply-To: <530E4B42.5090401@gmail.com> 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> From: Andy Lutomirski Date: Wed, 26 Feb 2014 12:26:43 -0800 Message-ID: Subject: Re: [PATCH v3 00/14] perf, x86: Haswell LBR call stack support To: David Ahern Cc: Andi Kleen , Stephane Eranian , "Yan, Zheng" , LKML , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 26, 2014 at 12:14 PM, David Ahern wrote: > On 2/26/14, 12:25 PM, Andy Lutomirski wrote: >> >> On Wed, Feb 26, 2014 at 11:19 AM, David Ahern wrote: >>> >>> On 2/26/14, 11:59 AM, Andy Lutomirski wrote: >>> >>>> I wonder if anyone who uses perf for userspace profiling *ever* uses >>>> FP and gets away with it. There's precious little userspace software >>>> compiled with frame pointers these days on most architectures. >>> >>> >>> >>> yes and yes. With control over the entire stack we are making sure >>> frame-pointers are enabled as much as possible. >>> >> >> I'm curious why. > > > Is there some reason not to enable frame pointers? 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. > > fp method has much less overhead than dwarf, and good, clear callchains are > important. > Agreed about the good, clear callchains. But DWARF seems to work pretty well, and you only have the overhead when you're actually debugging or profiling. > >> >> Maybe this should be a config option. Anyone using a standard distro >> is running a nearly completely frame-pointer-omitted userspace these >> days. > > > Does WRL or Yocto fall into that 'standard distro' comment? Fairly easy to > enable frame-pointers. Fair enough :) --Andy -- 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/