Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759432Ab0KQPlM (ORCPT ); Wed, 17 Nov 2010 10:41:12 -0500 Received: from mail-iw0-f174.google.com ([209.85.214.174]:49588 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759338Ab0KQPlK (ORCPT ); Wed, 17 Nov 2010 10:41:10 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=RJcGuM7Kzb2EI8KF8GPGek58BROk7L4gFEYTyFeT8DwfdM2j8YxYxMso4x7SZXHxcJ piwClh5XjlfbqPOdn7tyNVGIQGqkzi8E1XitB8tMH4kqTdf+RlLD07HhFkesR6MLmRkk RgesUSF0BoSfFgnatqbMLuqT/UhXXruAf06os= Subject: Re: [ANNOUNCE] New utility: 'trace' From: Tom Zanussi To: Thomas Gleixner Cc: Peter Zijlstra , Ingo Molnar , "Ted Ts'o" , LKML , Linus Torvalds , Andrew Morton , Steven Rostedt , Arjan van de Ven , Arnaldo Carvalho de Melo , Frederic Weisbecker , Masami Hiramatsu , Mathieu Desnoyers , Li Zefan , Jason Baron , "David S. Miller" , Christoph Hellwig , Pekka Enberg , Lai Jiangshan , Eric Dumazet In-Reply-To: References: <20101117013700.GA3290@thunk.org> <20101117132404.GF27063@elte.hu> <1290001128.2109.785.camel@laptop> <20101117140002.GH27063@elte.hu> <1290003110.2109.822.camel@laptop> <1290003505.2109.833.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Wed, 17 Nov 2010 09:41:06 -0600 Message-ID: <1290008466.1921.21.camel@elnicho> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2645 Lines: 62 On Wed, 2010-11-17 at 15:37 +0100, Thomas Gleixner wrote: > On Wed, 17 Nov 2010, Peter Zijlstra wrote: > > > On Wed, 2010-11-17 at 15:11 +0100, Peter Zijlstra wrote: > > > The idea was to not let the filter engine work on the trace data (once > > > its gathered) but on the trace argument right at the beginning of the > > > tracepoint callchain, since some of the trace data is an expression of > > > the trace argument (say next->prio instead of next), the trace > > > expression wouldn't stay invariant, you'd have to write a different > > > filter for the same effect. > > > > > > So I think it would be wise to make this change sooner rather than > > > later. > > > > Also, I see a lot of overlap with the dynamic probes stuff which needs > > the help of magic dwarves to come up with the right data to gather. > > > > Merging the dynamic tracepoint and filter stuff would be nice, there's > > no way you can express next->prio without the help of these short > > buggers with large axes. > > > > The trouble is that the dynamic tracepoint stuff is privileged for good > > reasons, try next+0x1000000 and you're out in the woods, priv. only > > filters otoh just doesn't sound too hot. > > > > Another nasty thing is that you actually need to have these dwarves > > present, which means having the -debug package installed. > > That sounds utterly insane for the basic use case where you trace > application context. There is no point to filter out the tracepoints, > really. Postprocessing can do that just fine. > > I consider myself a power user of tracing, but hell I never used any > of those filters in a real use case. awk, grep, scripting languages do > just a better job and you don't miss any data just because you got > your filter expression slightly wrong. Postprocessing always wins in > that regard. > > The only reason why these filters might make sense is to reduce the > trace volume on system wide traces in production environments, but > that's a completely different story. These scenarios can do with the > dynamic tracepoint stuff and the custom filtering w/o putting the > burden on the majority of users. > Yeah, in my mind, the main point of the filters was to be a 'blunt force' instrument preventing userspace from being overwhelmed by events. The real filtering would happen in userspace with e.g. real scripting languages. Tom > Thanks, > > tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/