Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762135AbZFKKWX (ORCPT ); Thu, 11 Jun 2009 06:22:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757623AbZFKKWP (ORCPT ); Thu, 11 Jun 2009 06:22:15 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:37741 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757280AbZFKKWO (ORCPT ); Thu, 11 Jun 2009 06:22:14 -0400 Date: Thu, 11 Jun 2009 12:21:59 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: "Metzger, Markus T" , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "hpa@zytor.com" , "oleg@redhat.com" , "tglx@linutronix.de" , "linux-tip-commits@vger.kernel.org" Subject: Re: [tip:tracing/core] Revert "x86, bts: reenable ptrace branch trace support" Message-ID: <20090611102159.GA31719@elte.hu> References: <928CFBE8E7CB0040959E56B4EA41A77EBBC6544B@irsmsx504.ger.corp.intel.com> <1244702183.6691.8.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1244702183.6691.8.camel@laptop> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2568 Lines: 60 * Peter Zijlstra wrote: > 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. Hm. Wrt. the ABI, wouldnt it make more sense to expose this PMU feature via perfcounters: a sampling hw-branch-executions counter, with interval=1. That would give the exact existing semantics, plus a lot lot more. Markus? Ingo -- 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/