From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753520AbaIXOVU (ORCPT ); Wed, 24 Sep 2014 10:21:20 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:52570 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751325AbaIXOVT (ORCPT ); Wed, 24 Sep 2014 10:21:19 -0400 Date: Wed, 24 Sep 2014 16:21:10 +0200 From: Peter Zijlstra To: kan.liang@intel.com Cc: eranian@google.com, linux-kernel@vger.kernel.org, mingo@redhat.com, paulus@samba.org, acme@kernel.org, ak@linux.intel.com, "Yan, Zheng" Subject: Re: [PATCH V5 14/16] perf, x86: enable LBR callstack when recording callchain Message-ID: <20140924142110.GG2805@worktop.programming.kicks-ass.net> References: <1410358153-421-1-git-send-email-kan.liang@intel.com> <1410358153-421-15-git-send-email-kan.liang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1410358153-421-15-git-send-email-kan.liang@intel.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 10, 2014 at 10:09:11AM -0400, kan.liang@intel.com wrote: > From: Kan Liang > > If a task specific event wants user space callchain but does not want > branch stack sampling, enable the LBR call stack facility implicitly. > The LBR call stack facility can help perf to get user space callchain > in case of there is no frame pointer. > > Note: this feature only affects how to get user callchain. The kernel > callchain is always got by frame pointers. Yeah, don't like this either. Suppose you have sane userspace (with framepointers enabled) then you're now loosing the better option.