From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758947AbZBXRSd (ORCPT ); Tue, 24 Feb 2009 12:18:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757377AbZBXRSZ (ORCPT ); Tue, 24 Feb 2009 12:18:25 -0500 Received: from mx2.redhat.com ([66.187.237.31]:40342 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757364AbZBXRSY (ORCPT ); Tue, 24 Feb 2009 12:18:24 -0500 Date: Tue, 24 Feb 2009 12:17:18 -0500 From: Jason Baron To: Frederic Weisbecker Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Steven Rostedt , Lai Jiangshan , Peter Zijlstra , Arnaldo Carvalho de Melo Subject: Re: [PATCH 0/3] tracing/ftrace: ftrace_bprintk Message-ID: <20090224171718.GA3189@redhat.com> References: <20090224051618.GA5142@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090224051618.GA5142@nowhere> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 24, 2009 at 06:16:18AM +0100, Frederic Weisbecker wrote: > Hi, > > These three patches are part of a patchset posted by Lai Jiangshan in december 2008. > They introduce a binary version of ftrace_printk() called ftrace_bprintk() > > While having the same goal: print a generic message entry into the ring buffer, > their approaches are very different. > > - ftrace_printk() does the formatting job on tracing time, insert the whole resulting string > into the ring buffer, and then the string is printed on output time without a lot of modifications. > > - ftrace_bprintk() does no formatting on tracing time. Instead, it looks at the format string > to find the types and the numbers of the arguments and directly stores them as-is into the > ring-buffer. Then the format string is stored into the ring-buffer too, but only by its address, > it is not copied. Then on output time only, the final string is formatted and sent to the user. > This gives a result about as fast as a traditional tracer with fixed fields types, except that > we can print random types and numbers of fields here. > > > The first patch adds the generic support for binary formatting. > The second adds the support for binary print types on ftrace > and the last introduces ftrace_bprintk() which supports safely the modules > by listening on the module loading/unloading notifier to keep track of > unwanted freed format strings. > > Lai Jiangshan (3): > add binary printf > ftrace: infrastructure for supporting binary record > ftrace: add ftrace_bprintk() > hi, this seems like a really valuable feature....I'm just wondering about a couple of things.... If the 'brpintk tracer' in trace/trace_bprintk.c is just being used to set an enabled flag for printing out these binary records, then are we better off with just an option flag in the 'trace_options' file? Second, can we somehow combine ftrace_printk() and ftrace_bprintk(), so that a developer can just use one interface? Perhaps, ftrace_printk calls ftrace_bprintk if binary option flag is set, otherwise, it just outputs things normally. thanks, -Jason