Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758722Ab3EFWnI (ORCPT ); Mon, 6 May 2013 18:43:08 -0400 Received: from mail-oa0-f52.google.com ([209.85.219.52]:59906 "EHLO mail-oa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757537Ab3EFWnF (ORCPT ); Mon, 6 May 2013 18:43:05 -0400 MIME-Version: 1.0 In-Reply-To: <20130506185226.GA17723@dyad.programming.kicks-ass.net> References: <1366844694-2770-1-git-send-email-andi@firstfloor.org> <1366844694-2770-2-git-send-email-andi@firstfloor.org> <20130502073720.GH7521@dyad.programming.kicks-ass.net> <20130506185226.GA17723@dyad.programming.kicks-ass.net> Date: Tue, 7 May 2013 00:43:04 +0200 Message-ID: Subject: Re: [PATCH 2/2] perf, x86: Don't allow unusual PEBS raw flags From: Stephane Eranian To: Peter Zijlstra Cc: Andi Kleen , Ingo Molnar , LKML , stable@vger.kernel.org, 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: 1793 Lines: 40 On Mon, May 6, 2013 at 8:52 PM, Peter Zijlstra wrote: > On Mon, May 06, 2013 at 07:44:19PM +0200, Stephane Eranian wrote: >> On Thu, May 2, 2013 at 9:37 AM, Peter Zijlstra wrote: >> > On Wed, Apr 24, 2013 at 04:04:54PM -0700, Andi Kleen wrote: >> >> From: Andi Kleen >> >> >> >> The PEBS documentation in the Intel SDM 18.6.1.1 states: >> >> >> >> """ >> >> PEBS events are only valid when the following fields of IA32_PERFEVTSELx are all >> >> zero: AnyThread, Edge, Invert, CMask. >> >> """ >> >> >> >> Since we had problems with this earlier, don't allow cmask, any, edge, invert >> >> as raw events, except for the ones explicitly listed as pebs_aliases. >> > >> > If its a simple matter of crap in crap out without affecting anything else we >> > shouldn't do anything. >> > >> The problem here is that you are sampling an instruction which did not cause >> the event you are measuring. Remember that using cmask, changes the >> nature of what's being measured (from event to cycles). > > Yeah.. I don't see the problem though. If you're using cmask and the like > you're supposed to know wth you're doing; which includes knowing your cpu and > what it thinks of such an event. > But that implies that you'd know that on Intel precise mode uses PEBS and that PEBS does not take cmask events. That seems to contradict the philosophy of perf_events where the kernel does the work for you. > The only reason to disallow events is if they (badly) interact with other > counters. -- 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/