Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757803AbZFJNno (ORCPT ); Wed, 10 Jun 2009 09:43:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754397AbZFJNng (ORCPT ); Wed, 10 Jun 2009 09:43:36 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:56788 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754330AbZFJNnf (ORCPT ); Wed, 10 Jun 2009 09:43:35 -0400 Subject: RE: [tip:tracing/core] x86, bts: reenable ptrace branch trace support From: Peter Zijlstra To: "Metzger, Markus T" Cc: Ingo Molnar , "mingo@redhat.com" , "hpa@zytor.com" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "oleg@redhat.com" , "linux-tip-commits@vger.kernel.org" In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77EBBC651F4@irsmsx504.ger.corp.intel.com> References: <20090424094448.A30216@sedona.ch.intel.com> <1244637843.13761.11786.camel@twins> <20090610125108.GA13506@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77EBBC651E2@irsmsx504.ger.corp.intel.com> <1244640558.13761.11833.camel@twins> <928CFBE8E7CB0040959E56B4EA41A77EBBC651F4@irsmsx504.ger.corp.intel.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 10 Jun 2009 15:43:31 +0200 Message-Id: <1244641411.13761.11850.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1980 Lines: 45 On Wed, 2009-06-10 at 14:32 +0100, Metzger, Markus T wrote: > >-----Original Message----- > >From: Peter Zijlstra [mailto:peterz@infradead.org] > >Sent: Wednesday, June 10, 2009 3:29 PM > >To: Metzger, Markus T > >Cc: Ingo Molnar; mingo@redhat.com; hpa@zytor.com; linux-kernel@vger.kernel..org; tglx@linutronix.de; > >oleg@redhat.com; linux-tip-commits@vger.kernel.org > >Subject: RE: [tip:tracing/core] x86, bts: reenable ptrace branch trace support > > > >On Wed, 2009-06-10 at 14:22 +0100, Metzger, Markus T wrote: > >> > >> The Debug Store interface is completely in-kernel. It does not expose > >> anything to the outside world. > >> > >> What we expose is a ptrace interface for branch tracing. > >> That this is built on top of Debug Store is completely hidden. > >> The Debug Store interface may be changed without impacting the > >> user-visible part at any time. > >> > >> I do think that a ptrace interface makes sense since debuggers are the > >> targeted users for branch tracing. > >> > >> I don't see why we should not merge the fixes now and then rework the > >> in-kernel parts as needed for supporting PEBS. > > > >Ok, so what is all that account_locked_memory() for? > > To allow debuggers (users) to decide how much memory they want to spend > on branch tracing. But that is the debug store, right? User visible through some mlock accounting and limit. Furthermore, it appears there is an interface for setting the size, that's also user visible and not fixable after the fact. Once you want to multiplex cpu-wide and per task BTS/PEBS contexts, there is no choice but to view the DS as a cpu resource, not a task resource, therefore you cannot specify a size, nor attribute it to specific tasks mm accounting. -- 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/