From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21543 invoked by alias); 6 Jul 2008 18:05:06 -0000 Received: (qmail 21536 invoked by uid 22791); 6 Jul 2008 18:05:05 -0000 X-Spam-Status: No, hits=-2.4 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (66.187.233.31) by sourceware.org (qpsmtpd/0.31) with ESMTP; Sun, 06 Jul 2008 18:04:47 +0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id m66I1KWS003548; Sun, 6 Jul 2008 14:01:20 -0400 Received: from pobox-3.corp.redhat.com (pobox-3.corp.redhat.com [10.11.255.67]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m66I1Kxu027278; Sun, 6 Jul 2008 14:01:20 -0400 Received: from touchme.toronto.redhat.com (IDENT:postfix@touchme.yyz.redhat.com [10.15.16.9]) by pobox-3.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m66I0c86022364; Sun, 6 Jul 2008 14:01:11 -0400 Received: from ton.toronto.redhat.com (ton.yyz.redhat.com [10.15.16.15]) by touchme.toronto.redhat.com (Postfix) with ESMTP id E7CA48001FF; Sun, 6 Jul 2008 14:00:21 -0400 (EDT) Received: from ton.toronto.redhat.com (localhost.localdomain [127.0.0.1]) by ton.toronto.redhat.com (8.13.1/8.13.1) with ESMTP id m66I05ax023503; Sun, 6 Jul 2008 14:00:05 -0400 Received: (from fche@localhost) by ton.toronto.redhat.com (8.13.1/8.13.1/Submit) id m66I03p6023475; Sun, 6 Jul 2008 14:00:03 -0400 X-Authentication-Warning: ton.toronto.redhat.com: fche set sender to fche@redhat.com using -f To: Evgeniy Polyakov Cc: Christoph Hellwig , ksummit-2008-discuss@lists.linux-foundation.org, systemtap@sources.redhat.com Subject: Re: [Ksummit-2008-discuss] DTrace References: <20080627155018.GC14894@parisc-linux.org> <1214583502.7698.15.camel@weaponx> <20080627163056.GB1416@lst.de> <20080628072605.GA505@in.ibm.com> <20080629084002.GA24131@lst.de> <20080630051034.GA4970@in.ibm.com> <20080630112913.GA18817@lst.de> <20080630171246.GB21660@redhat.com> <20080706123414.GA9265@lst.de> <20080706154612.GL2881@redhat.com> <20080706163533.GA16721@2ka.mipt.ru> From: fche@redhat.com (Frank Ch. Eigler) Date: Sun, 06 Jul 2008 18:05:00 -0000 In-Reply-To: <20080706163533.GA16721@2ka.mipt.ru> (Evgeniy Polyakov's message of "Sun, 6 Jul 2008 20:35:34 +0400") Message-ID: User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Scanned-By: MIMEDefang 2.58 on 172.16.52.254 Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2008-q3/txt/msg00056.txt.bz2 Evgeniy Polyakov writes: >> > We don't add kernel interface for out of tree modules. >> >> That is a specific example of an attitude that I hope will be >> reexamined if y'all want to support dtrace-level introspection. > > I believe the only answer you will get is 'no'. Both for dtrace-like > stuff and ability to add unmaintained interfaces into the kernel. > > Out-of-tree stuff can appear and disappear, change its internal > structures, API, ABI [...] Yes, well, it turns out that the number of systemtap-specific kernel interfaces we have requested is ... precisely ... zero. We have on occasion asked that some established module interfaces simply not be *unexported*, but almost all of those requests have been turned down, requiring us to kludge. We have helped promote a systemtap-neutral instrumentation mechanism (markers), along with a project with a near-decade history of stable instrumentation (ltt/ng), and one can see the progress (?) that this has made even since Karim's "emperor is naked" note two (!) years ago. >> > And thinking about it - having to compile out of tree kernel modules >> > on the fly to trace user space processes is just braindead. >> >> I gladly grant "counterintuitive", especially if one's intuition is >> limited to probing just one's own pet user-space process. It is a >> different matter when one needs to seamlessly probe a mixture of >> kernel activities, daemons, and user processes. > > Out of curiosity, how in the hell administrator or any other non kernel > hacker person needs to have ability to tap into userspace process via > kernel module? Think about how a non-intrusive system-wide probing must work, if it is desirable not to interfere with e.g. thread scheduling or VM state. Specifically, if we don't want to context-switch from threads (thereby interfering with contention effects we may want to measure), nor page data in/out just to satisfy probe data (thereby generating more I/O and associated distortions). It seems only kernel-side code can do all of that. Do you have a better suggestion? - FChE