Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755344AbaKERk5 (ORCPT ); Wed, 5 Nov 2014 12:40:57 -0500 Received: from mga02.intel.com ([134.134.136.20]:33101 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755269AbaKERkx (ORCPT ); Wed, 5 Nov 2014 12:40:53 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,321,1413270000"; d="scan'208";a="602892781" Date: Wed, 5 Nov 2014 09:40:31 -0800 From: Andi Kleen To: Stephane Eranian Cc: Peter Zijlstra , Kan Liang , LKML , "mingo@redhat.com" , Paul Mackerras , Arnaldo Carvalho de Melo , Jiri Olsa Subject: Re: [PATCH V7 13/17] perf, x86: enable LBR callstack when recording callchain Message-ID: <20141105174031.GO3274@tassilo.jf.intel.com> References: <1415156173-10035-1-git-send-email-kan.liang@intel.com> <1415156173-10035-14-git-send-email-kan.liang@intel.com> <20141105092145.GP10501@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > The reason why using LBR call stack mode is restricted to user level > only is because of > a bug in the LBR call stack hardware which forces the kernel to drop > LBR_FREEZE_PMI. It works with PEBS events, just not with non PEBS (the patch currently does not implement this distinction and I'm not sure it's worth it) > In other words ,the LBR does not stop on counter overflow, thus it > will be wiped out by > execution of kernel code leading to the PMU interrupt handler. It stops, but it takes some time to stop so the call-return stack can get out of sync. -Andi -- ak@linux.intel.com -- Speaking for myself only -- 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/