Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759131AbZFKHSK (ORCPT ); Thu, 11 Jun 2009 03:18:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756264AbZFKHR5 (ORCPT ); Thu, 11 Jun 2009 03:17:57 -0400 Received: from mga02.intel.com ([134.134.136.20]:1046 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753036AbZFKHR4 convert rfc822-to-8bit (ORCPT ); Thu, 11 Jun 2009 03:17:56 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.42,201,1243839600"; d="scan'208";a="420762725" From: "Metzger, Markus T" To: Peter Zijlstra CC: "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "hpa@zytor.com" , "oleg@redhat.com" , "tglx@linutronix.de" , "mingo@elte.hu" , "linux-tip-commits@vger.kernel.org" Date: Thu, 11 Jun 2009 08:17:53 +0100 Subject: RE: [tip:tracing/core] Revert "x86, bts: reenable ptrace branch trace support" Thread-Topic: [tip:tracing/core] Revert "x86, bts: reenable ptrace branch trace support" Thread-Index: AcnqXvjBFiELrYUYQBiDMzLNqrQ7lgAARmpg Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EBBC6546E@irsmsx504.ger.corp.intel.com> References: <928CFBE8E7CB0040959E56B4EA41A77EBBC6544B@irsmsx504.ger.corp.intel.com> <1244702183.6691.8.camel@laptop> In-Reply-To: <1244702183.6691.8.camel@laptop> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3818 Lines: 87 >-----Original Message----- >From: Peter Zijlstra [mailto:peterz@infradead.org] >Sent: Thursday, June 11, 2009 8:36 AM >To: Metzger, Markus T >Cc: linux-kernel@vger.kernel.org; mingo@redhat.com; hpa@zytor.com; oleg@redhat.com; >tglx@linutronix.de; mingo@elte.hu; linux-tip-commits@vger.kernel.org >Subject: RE: [tip:tracing/core] Revert "x86, bts: reenable ptrace branch trace support" > >On Thu, 2009-06-11 at 07:30 +0100, Metzger, Markus T wrote: >> >-----Original Message----- >> >From: tip-bot for Ingo Molnar [mailto:mingo@elte.hu] >> >Sent: Thursday, June 11, 2009 1:37 AM >> >To: linux-tip-commits@vger.kernel.org >> >Cc: hpa@zytor.com; mingo@redhat.com; peterz@infradead.org; Metzger, Markus T; oleg@redhat.com; >> >tglx@linutronix.de; mingo@elte.hu >> >Subject: [tip:tracing/core] Revert "x86, bts: reenable ptrace branch trace support" >> > >> >Commit-ID: 511b01bdf64ad8a38414096eab283c7784aebfc4 >> >Gitweb: http://git.kernel.org/tip/511b01bdf64ad8a38414096eab283c7784aebfc4 >> >Author: Ingo Molnar >> >AuthorDate: Thu, 11 Jun 2009 00:32:00 +0200 >> >Committer: Ingo Molnar >> >CommitDate: Thu, 11 Jun 2009 00:32:00 +0200 >> > >> >Revert "x86, bts: reenable ptrace branch trace support" >> > >> >This reverts commit 7e0bfad24d85de7cf2202a7b0ce51de11a077b21. >> > >> >A late objection to the ABI has arrived: >> > >> > http://lkml.org/lkml/2009/6/10/253 >> >> I thought that this has been resolved. See for example http://lkml.org/lkml/2009/6/10/257. >> >> Peters concerns were that Debug Store details are exposed to user space, which is >> not the case. Debug Store itself is fully in-kernel and the expectation of a >> user-defined buffer can be implemented on top of the Debug Store changes that >> Peter expects are needed to support PEBS. >> >> A user-defined trace buffer size is required to support different usage models. >> Some users only need a small amount of trace, whereas others need a big amount. >> The interface will have to reflect that in some way. > >Right, your last email did explain how we could keep per task in-kernel >buffers and fill them from the DS and still have them of user-specified >size. > >That would indeed keep the proposed ABI workable, what I'm still not >liking is that this buffer is in-kernel, but I guess that might be >something for other people to have an opinion on. The alternative would be to give a user-allocated buffer to the tracing h/w. We would need to take precautions to prevent the user from messing around with that buffer while the h/w is writing to it. Other code uses the kernel- allocated buffer plus copy_to_user() approach, as well. Further, it would require the user to interpret the various tracing formats, whereas the existing interface provides an architecture-independent format. Does anybody have concerns on using an in-kernel buffer and providing a copy_to_user() interface? regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). 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