From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756278AbZCZIIt (ORCPT ); Thu, 26 Mar 2009 04:08:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753336AbZCZII1 (ORCPT ); Thu, 26 Mar 2009 04:08:27 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:44234 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756196AbZCZIIU (ORCPT ); Thu, 26 Mar 2009 04:08:20 -0400 Date: Thu, 26 Mar 2009 09:07:57 +0100 From: Ingo Molnar To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Mike Galbraith , Arjan van de Ven Subject: Re: [PATCH 0/2] [GIT PULL] function profiler updates Message-ID: <20090326080757.GA616@elte.hu> References: <20090326010737.611522983@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090326010737.611522983@goodmis.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean 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=3.2.3 -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 * Steven Rostedt wrote: > > Ingo, > > Please pull the latest rfc/tip/tracing/function-profiler tree, which can be found at: > > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git > rfc/tip/tracing/function-profiler > > > Steven Rostedt (2): > tracing: remove on the fly allocator from function profiler > tracing: add average time in function to function profiler > > ---- > kernel/trace/ftrace.c | 97 +++++++++++++++++++++++++++++-------------------- > 1 files changed, 57 insertions(+), 40 deletions(-) > -- Pulled, thanks Steve. The on-the-fly allocator was my main conceptual worry about this. How useful this kind of profiling will end up being in practice remains to be seen - but it does have a handful of unique properties that cannot be dismissed. It's main downside is its overhead - sampling based profilers are a lot more lightweight and allow unintrusive inspection of workloads. The upside of it are all the things that this profiling overhead allows us to do: - 100% precise, non-sampling profiling - accurate profiles possible with very short, bursty workloads too - filtering capabilities of the tracing subsystem allow the flexible shaping of the set of functions and the set of conditions that are profiled: there's the regex filter and there's also the tracepoint based filter expressions. - it also allowsuser-space driven filtering: if user-space wants to profile just one specific functionality (say the function calls of one specific library), they can use /debug/tracing/enabled fast toggle to turn profiling on/off runtime. This can be done at a very high frequency as well. - developers can switch between profiling and tracing mode seemlessly. This allows multiple 'dimensions' of the same workload to be observed, via the same set of facilities. Ingo