Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751843Ab3FYMlA (ORCPT ); Tue, 25 Jun 2013 08:41:00 -0400 Received: from mail-oa0-f54.google.com ([209.85.219.54]:42845 "EHLO mail-oa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751729Ab3FYMk7 (ORCPT ); Tue, 25 Jun 2013 08:40:59 -0400 MIME-Version: 1.0 In-Reply-To: <1372150039-15151-1-git-send-email-zheng.z.yan@intel.com> References: <1372150039-15151-1-git-send-email-zheng.z.yan@intel.com> Date: Tue, 25 Jun 2013 14:40:58 +0200 Message-ID: Subject: Re: [PATCH 0/7] perf, x86: Haswell LBR call stack support From: Stephane Eranian To: "Yan, Zheng" Cc: LKML , Ingo Molnar , Peter Zijlstra , Andi Kleen Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1440 Lines: 29 On Tue, Jun 25, 2013 at 10:47 AM, Yan, Zheng wrote: > From: "Yan, Zheng" > > Haswell has a new feature that utilizes the existing Last Branch Record > facility to record call chains. When the feature is enabled, function > call will be collected as normal, but as return instructions are executed > the last captured branch record is popped from the on-chip LBR registers. > The LBR call stack facility can help perf to get call chains of progam > without frame pointer. When perf tool requests PERF_SAMPLE_CALLCHAIN + > PERF_SAMPLE_BRANCH_USER, this feature is dynamically enabled by default. > This feature can be disabled/enabled through an attribute file in the cpu > pmu sysfs directory. > > The LBR call stack has following known limitations > 1. Zero length calls are not filtered out by hardware > 2. Exception handing such as setjmp/longjmp will have calls/returns not > match > 3. Pushing different return address onto the stack will have calls/returns > not match > I would also add that it does not work with leaf call optimizations: A calls B, B calls C, C returns to A and that can be fairly common with small functions. -- 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/