From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 27276 invoked by alias); 1 Nov 2010 17:32:08 -0000 Received: (qmail 27268 invoked by uid 22791); 1 Nov 2010 17:32:07 -0000 X-SWARE-Spam-Status: No, hits=-5.8 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,SPF_HELO_PASS,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 01 Nov 2010 17:32:02 +0000 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id oA1HW1pB024571 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 1 Nov 2010 13:32:01 -0400 Received: from fche.csb (vpn-8-165.rdu.redhat.com [10.11.8.165]) by int-mx02.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id oA1HW03S011238; Mon, 1 Nov 2010 13:32:01 -0400 Received: by fche.csb (Postfix, from userid 2569) id 4418A5812F; Mon, 1 Nov 2010 13:32:00 -0400 (EDT) To: Grant Edwards Cc: systemtap@sources.redhat.com Subject: Re: documentation for user-space usage? References: From: fche@redhat.com (Frank Ch. Eigler) Date: Mon, 01 Nov 2010 17:32:00 -0000 In-Reply-To: (Grant Edwards's message of "Mon, 1 Nov 2010 14:42:44 +0000 (UTC)") Message-ID: User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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: 2010-q4/txt/msg00139.txt.bz2 grant.b.edwards wrote: > [...] > Assuming utrace/uprobes gets ported to ARM, does such a trace events > involve a context switch to kernel-mode and then back to user-mode? Yes. > [...] I'm using ARM9. Utrace support patches have apparently been > rejected by the kernel maintainers, so I'd hae to maintain my own > fork of the kernel as well as port uprobes. I think. How close is your current kernel to fedora's? >> [...] User-space probing and kernel-space probing are basically identical >> from the point of view of the stap user. > > Is the timing impact of a user-space probe no different than that of a > kernel-space probe? It's very similar. >> [...] >> The theoretical fit is pretty good. If in practice you are blocked >> by some missing unported layer, you could decide between helping >> port, prototyping on x86 while someone else ports, and/or >> investigating other logging-related tools/libraries. > > I wouldn't mind working on porting uprobes if I was confident that it > would be accepted upstream. Since utrace support was apparently not > accepted, I'm not too optimistic. Another option is to go ahead and try to port uprobes, leave ARM/utrace to us / fedora people. When/if the newer lkml-track uprobes gets merged, the hypothetical ARM port could go into the main kernel that way, bypassing the utrace kerfuffle. IOW, doing an ARM port of the current systemtap-resident uprobes would not be a wasted effort, if LKML gets its act together and merges the other one. - FChE