From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22029 invoked by alias); 20 Oct 2006 00:27:58 -0000 Received: (qmail 22021 invoked by uid 22791); 20 Oct 2006 00:27:57 -0000 X-Spam-Status: No, hits=-1.2 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS,UNPARSEABLE_RELAY 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; Fri, 20 Oct 2006 00:27:54 +0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.12.11.20060308/8.12.11) with ESMTP id k9K0RrqU030412; Thu, 19 Oct 2006 20:27:53 -0400 Received: from pobox.toronto.redhat.com (pobox.toronto.redhat.com [172.16.14.4]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id k9K0RqBD014360; Thu, 19 Oct 2006 20:27:52 -0400 Received: from touchme.toronto.redhat.com (IDENT:postfix@touchme.toronto.redhat.com [172.16.14.9]) by pobox.toronto.redhat.com (8.12.11.20060308/8.12.11) with ESMTP id k9K0Rq4A021360; Thu, 19 Oct 2006 20:27:52 -0400 Received: from ton.toronto.redhat.com (ton.toronto.redhat.com [172.16.14.15]) by touchme.toronto.redhat.com (Postfix) with ESMTP id 42CFD800002; Thu, 19 Oct 2006 20:27:52 -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 k9K0RpGf031782; Thu, 19 Oct 2006 20:27:51 -0400 Received: (from fche@localhost) by ton.toronto.redhat.com (8.13.1/8.13.1/Submit) id k9K0RpAt031781; Thu, 19 Oct 2006 20:27:51 -0400 Date: Fri, 20 Oct 2006 00:27:00 -0000 From: "Frank Ch. Eigler" To: David Boreham Cc: systemtap@sources.redhat.com Subject: Re: user mode backtrace Message-ID: <20061020002751.GG4201@redhat.com> References: <4537E44C.6040604@boreham.org> <45381525.7000100@boreham.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45381525.7000100@boreham.org> User-Agent: Mutt/1.4.1i Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2006-q4/txt/msg00208.txt.bz2 Hi - On Thu, Oct 19, 2006 at 06:15:33PM -0600, David Boreham wrote: > >[...] one where the compiled systemtap probes get some extract of > >backtrace-enabling unwind information [...]; and another one where > >the probe may snapshot only an approximation [...] and rely on a > >user-space helper to correct/complete it [...] > Given the choice I'd prefer the latter because it'd be less intrusive. Actually, intrusiveness is probably not the real trade-off point. Both approaches would require scanning the user-space stack. The former (the probe knowing unwind info) might even be lighter, in that it would know which portions of the stack need to be sampled. The latter may need to be conservative and transcribe a larger number of words. With respect to speed, unwinding vs. conservative sampling should not be too different. The trade-offs are probably closer to issues such as expressiveness, module size, complexity of kernel/user interaction. - FChE