From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 3709 invoked by alias); 24 Jan 2013 16:17:42 -0000 Received: (qmail 3696 invoked by uid 22791); 24 Jan 2013 16:17:40 -0000 X-SWARE-Spam-Status: No, hits=-7.7 required=5.0 tests=AWL,BAYES_00,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_DNSWL_HI,RCVD_IN_HOSTKARMA_W,RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mga09.intel.com (HELO mga09.intel.com) (134.134.136.24) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 24 Jan 2013 16:17:34 +0000 Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga102.jf.intel.com with ESMTP; 24 Jan 2013 08:16:23 -0800 X-ExtLoop1: 1 Received: from irsmsx103.ger.corp.intel.com ([163.33.3.157]) by orsmga001.jf.intel.com with ESMTP; 24 Jan 2013 08:17:28 -0800 Received: from irsmsx151.ger.corp.intel.com (163.33.192.59) by IRSMSX103.ger.corp.intel.com (163.33.3.157) with Microsoft SMTP Server (TLS) id 14.1.355.2; Thu, 24 Jan 2013 16:17:27 +0000 Received: from irsmsx102.ger.corp.intel.com ([169.254.2.82]) by IRSMSX151.ger.corp.intel.com ([169.254.4.144]) with mapi id 14.01.0355.002; Thu, 24 Jan 2013 16:17:27 +0000 From: "Metzger, Markus T" To: Ingo Molnar CC: "mingo@redhat.com" , "mingo@elte.hu" , "linux-kernel@vger.kernel.org" , Mark Kettenis , Pedro Alves , Jan Kratochvil , "gdb-patches@sourceware.org" Subject: RE: [PATCH] x86, perf, bts: disable BTS from Nehalem to Ivy Bridge Date: Thu, 24 Jan 2013 16:17:00 -0000 Message-ID: References: <1354876511-25294-1-git-send-email-markus.t.metzger@intel.com> <20130124154637.GB32146@gmail.com> In-Reply-To: <20130124154637.GB32146@gmail.com> Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2013-01/txt/msg00596.txt.bz2 > -----Original Message----- > From: gdb-patches-owner@sourceware.org [mailto:gdb-patches-owner@sourcewa= re.org] On Behalf Of Ingo Molnar > Sent: Thursday, January 24, 2013 4:47 PM > > Starting with Nehalem, the BTS "from" information may in some cases be > > incorrect (AAJ122). > > > > This has been detected while adding branch tracing support to gdb, wher= e it > > results in sporadic test fails. > > > > Disable BTS support on Nehalem, Westmere, Sandy Bridge, and Ivy Bridge. >=20 > But the failures are rare, so the BTS data is still correct > statistically, by and large, right? So why not just keep it > as-is and teach tooling to be more robust about implausible > trace entries? It has to be ready for that eventuality *anyway*. Yes, the fails are rare. They are frequent enough, however, to cause sporad= ic test fails. The problem is that you can't reliably detect such fails. In the worst case= , GDB would show wrong but plausible trace. Typically, GDB just shows garba= ge (i.e. impossible trace) in such cases. I'm afraid one might endlessly debate whether the feature as-is is useful o= r not. It is working fine on Atom so I chose to disable it on core. The GDB folks would rather not disable the feature inside GDB; they prefer = that it is disabled in the kernel. There will be an additional check inside= GDB to support older kernel versions. Regards, markus. Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen, Deutschland Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Christian Lamprechter, Hannes Schwaderer, Douglas Lusk Registergericht: Muenchen HRB 47456 Ust.-IdNr./VAT Registration No.: DE129385895 Citibank Frankfurt a.M. (BLZ 502 109 00) 600119052