From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758000AbYDRGq6 (ORCPT ); Fri, 18 Apr 2008 02:46:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753592AbYDRGqu (ORCPT ); Fri, 18 Apr 2008 02:46:50 -0400 Received: from viefep18-int.chello.at ([213.46.255.22]:54376 "EHLO viefep19-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752023AbYDRGqt (ORCPT ); Fri, 18 Apr 2008 02:46:49 -0400 Subject: Re: [RFC PATCH 1/2] Marker probes in futex.c From: Peter Zijlstra To: "Frank Ch. Eigler" Cc: prasad@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu, mathieu.desnoyers@polymtl.ca In-Reply-To: References: <20080415115058.GA6788@in.ibm.com> <20080415115314.GA6975@in.ibm.com> <1208260942.6395.6.camel@twins> <20080415155223.GA6935@in.ibm.com> <1208361092.6395.81.camel@twins> Content-Type: text/plain Date: Fri, 18 Apr 2008 08:46:44 +0200 Message-Id: <1208501204.7115.60.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.22.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2008-04-17 at 18:02 -0400, Frank Ch. Eigler wrote: > Peter Zijlstra writes: > > > [...] > >> If we were to log just the futex_ops, just as you had suggested, > >> "Just log: > >> > >> futex: wait > >> futex: wakeup" > >> [...] > >> If you can specifically point me to information you think would be > >> absolutely unnecessary, I can get them out of the trace_mark(). > > > > I'm thinking everything is superflous; you're basically logging what > > strace already gives you > > But we don't want to run strace just for this stuff. As you probably > know, strace involves invasive user-space context-switching between > the target and the tracer. > > > except worse by encoding local variable names and exposing kernel > > pointers. > > The pointers are probably excessive, the and the names don't really > matter. Then what do we do when someone comes along and changes one of those names; do we go around changing the markers and then requiring all tools to change as well? (And no this isn't far fetched; I'm thinking of changing fshared in the near future). Sounds like people will complain and generate back pressure against such changes - something we should avoid. As soon as these markers place a significant burden on code maintenance I'm against it. > What does matter is providing enough information for a > problem diagnosis tool & person to reconstruct what the kernel must > have been thinking when it did something noteworthy. Sure, but then just make a strace like tracer and be done with it - no need to pollute the futex code with that.